STRUCTURAL ANALYSIS AND RECONSTRUCTION OF THE SOUTHERN END OF THE PUMPKIN HOLLOW DEPOSIT, YERINGTON DISTRICT, NEVADA. Mariel Taylor Schottenfeld

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1 STRUCTURAL ANALYSIS AND RECONSTRUCTION OF THE SOUTHERN END OF THE PUMPKIN HOLLOW DEPOSIT, YERINGTON DISTRICT, NEVADA by Mariel Taylor Schottenfeld A Prepublication Manuscript submitted to the Faculty of the DEPARTMENT OF GEOSCIENCES In Partial Fulfillment of the Requirements For the Degree of MASTER OF SCIENCE In the Graduate College THE UNIVERSITY OF ARIZONA 2012

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3 Reconstruction of the southern end of the Pumpkin Hollow deposit, Yerington district, Nevada Abstract This study characterizes the major post-ore faults in the vicinity of the South and Southeast ore bodies in the southern part of the Pumpkin Hollow deposit using data from core logs, preexisting geologic maps, and original geologic maps of two new trenches across two of the major faults. The purpose of the study is to constrain the direction and amount of slip on the faults and to test the hypothesis that the South and Southeast ore bodies were contiguous prior to normal faulting. Pumpkin Hollow is an iron-oxide-copper-gold (IOCG) deposit that is hosted by Mesozoic sedimentary rocks. The deposit is owned by the Nevada Copper Corporation, and located on the edge of the Yerington district, western Nevada. The deposit consists of Fe-Cu skarn and massive replacement bodies formed beyond the southeastern fringe of the Middle Jurassic Yerington batholith. The Pumpkin Hollow deposit formed at ~168 Ma broadly contemporaneous with, but distal to, the porphyry copper systems in the district. The Pumpkin Hollow deposit is covered by Tertiary and younger rocks but is pierced by numerous drill holes, and the post-ore faults are exposed locally at the surface and in two trenches (GPS coordinates given in Appendix Figs. A1, A2). The major faults generally consist of 2-5 m of breccia and gouge in drill core. Structure contour maps and geologic maps of the hanging wall and footwall surfaces were constructed for each fault in the southern part of the deposit for which there are adequate data. These maps display the shapes of the faults and are used to constrain the magnitude and direction of slip, which may vary along strike. This study identifies six main faults: the Western fault (strikes N10-45W and dips E), the Middle 1

4 fault ( N10-35W, ENE), Western Flat fault (approximately flat, as observed in cross section), Upper Middle Flat fault (N20W, 27 NE), Middle Flat fault (N45W, 23 NE),and Lower Middle Flat fault (approximately flat, as observed in the hanging wall of the Middle fault), and there is another fault on the easternmost part of the property for which there is too little data to warrant detailed study at this time. The Middle and Western faults are exposed in the trenches and by drill holes, and drill holes best constrain the geometry of the Flat faults. Fault surface maps were constructed for each fault (except the LMF fault, for which too little data are available) to determine the shapes of the faults and to constrain the magnitude and direction of slip. A three-dimensional technique is used to make the structural reconstructions, which relies on the geologic maps of the hanging wall and footwall fault surfaces. Previous workers describe three sets of north-south striking, district-wide normal faults in the Yerington district, each of which initially dipped moderately to steeply east, that formed in three successive generations since 14 Ma. Faults in the first and oldest of these sets (e.g., Singatse fault) currently dip gently east or are slightly tilted beyond horizontal to the west. The Flat faults at Pumpkin Hollow, which are subhorizontal, appear to belong to this first set of normal faults and may represent higher faults in current orientation or more easterly members of the first set of faults. Faults in the second set (e.g., May Queen) currently dip ~30 E, and the Western and Middle faults appear to correlate with the second set of faults. Faults in the third and youngest set (e.g., Range Front fault on the eastern side of the Singatse Range) currently dip ~60 E, but no representative of the third set was positively identified in this study. The total amount of extension across the Pumpkin Hollow deposit is ~200%. The Southeast ore body likely would restore over the top of the South ore body and would have formed its upper, eastern continuation prior to faulting and associated tilting. 2

5 Introduction The origin of normal faulting in the Basin and Range province was a matter of controversy in structural geology for several decades. In part this was due to the unique geologic setting of the physiographic Basin and Range, for nowhere else on the Earth is there a greater magnitude of extension (Dickinson, 2002). In the 1960s-80s, research on normal faulting focused on the mechanics of the normal faults that occur throughout the North American Cordillera, many presently dipping at low angles (Wernicke, 2009). Timing, structural context, and geometry were all important features in these debates (Armstrong, 1972; Davis and Coney, 1979; Gans et al., 1985; Wernicke and Burchfiel, 1982), including whether the low-angle faults in eastern Nevada were related to the contractional Sevier orogeny to the east or were younger, denudational (extensional) phenomena (Armstrong, 1972). Problematic to many of these authors was the difficultly in explaining the observations that the normal faults appear to be younger than the thrust faults of the Sevier orogeny, yet the two were potentially linked in the eastern Great Basin. Around the same time, Proffett (1977) showed that the low-angle faults in the Yerington district of western Nevada are normal faults that formed at high angles but rotated as they moved and were further tilted passively when cut by younger, high-angle faults. Shortly thereafter, Coney and Harms (1984) melded the apparent inconsistencies of age and geologic relationships of the previous decade. Their conclusion was that the Sevier orogeny had overthickened the crust to the point of extensional collapse, resulting in Tertiary normal faulting in the present-day Basin and Range physiographic province. Understanding Cenozoic extension is critical to determining the post-mineralization placement of ore bodies in the Basin and Range province, including the highly mineralized 3

6 Yerington district. Indeed, many of the structural geologic studies in the Yerington district, including those of Proffett (1977), have been driven by mineral exploration. The district contains several porphyry copper centers that are principally the product of magmatic-hydrothermal fluids that were released during late stages of evolution of the Jurassic Yerington batholith. These copper deposits include the Anaconda-mined Yerington deposit, the Ann-Mason deposit, and the MacArthur and Bear deposits (Heatwole, 1978; Carten, 1986; Dilles, 1987; Dilles and Einaudi, 1992; Dilles et al., 2000; Quaterra Alaska, 2010), as well as nearby skarn and lode copper deposits (Einaudi, 1977, 2000; Harris and Einaudi, 1982). A second type of deposit formed broadly contemporaneous with the porphyry and copper skarn deposits but on the fringes of the porphyry centers and along the margins of the batholith. These deposits, which occur as skarns, massive replacement deposits, and lodes, contain abundant iron oxides (magnetite and hematite) and variable amounts of copper, gold, and silver. This second group of deposits includes the Buckskin (Gibson, 1987), Minnesota (Reeves et al., 1958), Blue Jay (Matlock and Ohlin, 1996; Dilles et al., 2010), Northern Lights (Dilles and Proffett, 1995), and Pumpkin Hollow (Lyon) (Smith, 1984; Matlock and Ohlin, 1996; Ohlin, 2010; Rozelle, 2010) deposits. These deposits have been interpreted to have formed by circulation of external brines (Dilles and Proffett, 1995; Dilles et al., 1995; Battles and Barton, 1995; Barton and Johnson, 1996; Dilles et al., 2000; Barton et al., 2011) and are classified as members of the iron oxide-copper-gold (IOCG) family of deposit (e.g., Barton and Johnson, 2000; Williams et al., 2005). The foundation for the geologic understanding of the Yerington district is high-quality geologic maps. Geologic maps completed during and soon following the Anaconda era include Proffett (1969, 1977), Proffett and Dilles (1984), Dilles (1987), and Dilles and Einaudi (1992). The four cross sections of Proffett and Dilles (1984) are focused on the western half of the map 4

7 that covers the central and western portions of the district, from Mason Valley through the Singatse Range toward the Buckskin Range. More recent published mapping in the area includes work to the west in the Buckskin Range (e.g., Lipske and Dilles, 2000) and eastward into the Wassuk Range along the northeastern (McIntyre, 1990; Dilles, 1993) and southeastern and southern (Surpless, 2010, 2012) edges of the district. Numerous normal faults, active beginning about 15 Ma and continuing discontinuously to the present day, have tilted the stratigraphic units of the Yerington district about and extended the region >150% (Proffett, 1977; Dilles and Gans, 1995; Stockli et al., 2002). Lithologic units once deeply buried are now exposed at the surface by normal faulting and associated tilting. In map view, the entire region can be viewed as a series of cross sections or paleodepth profiles of the district in Jurassic time. The map of Proffett and Dilles (1984) shows the distribution of and crosscutting relations between normal faults in the Yerington district, which can be grouped into three sets or generations of normal faults (Proffett, 1977; Dilles et al., 2000). The subject of this paper is the structural geology of a portion of the Pumpkin Hollow Property, an iron oxide-copper-(gold-silver) skarn with IOCG affiliations that is owned by the Nevada Copper Corporation and located in the southeastern part of the Yerington district. The deposit is entirely covered by post-ore volcanic and sedimentary rocks but is exposed by numerous drill holes. The principal purpose of this study is to characterize the major faults in the vicinity of the South and Southeast ore bodies in the southern part of the Pumpkin Hollow deposit using data from core logs, geologic maps, and original geologic maps of two new trenches across faults. 5

8 Location and Geologic Setting Location The Yerington district is situated within the Basin and Range physiographic province and is located between the Walker Lane strike-slip shear zone to the northeast and the Sierra Nevada block to the southwest (Proffett, 1977; Dilles, 1993; Dilles and Gans, 1995; Surpless, 2012). The district is located near the town of Yerington in Lyon County, western Nevada, and straddles portions of the Buckskin, Singatse, and Wassuk Ranges. The study area is on the eastern side of Mason Valley, southeast of the town of Yerington and between the Singatse and Wassuk Ranges (Fig. 1). Stratigraphy The Mesozoic stratigraphy of the Yerington district is documented by Proffett (1969), Einaudi (1977), and Proffett and Dilles (1984, 2008). The oldest units are Middle Triassic or older, and the youngest are Middle Jurassic (Fig. 2). The sequence consists, from oldest to youngest, of the McConnell Canyon Volcanics, the Malachite Mine Formation, the tuff of Western Nevada Mine, the Mason Valley Limestone, the Gardnerville Formation, the Ludwig Mine Formation (at Pumpkin Hollow, called the Ludwig Limestone), the Artesia Lake Volcanics, and the Fulstone Spring Volcanics (Proffett and Dilles, 2008). The McConnell Canyon Volcanics, which are Middle Triassic or older, consist of a lower andesite member and an upper rhyolite member, as well as quartz porphyry dikes and sills. The Late Triassic Malachite Mine Formation consists of a lower dolomitic limestone member, a middle black calcareous argillite member, and an upper volcanic sandstone and limestone member. The Late 6

9 Triassic tuff of the Western Nevada Mine contains rhyolitic and andesitic tuffaceous rocks. This unit is not as easily correlated across the Yerington district as other units. The Late Triassic Mason Valley Limestone, which is the principal host of mineralization at Pumpkin Hollow, consists of a lower massive pale limestone overlain by an upper darker, thinly bedded limestone. The Late Triassic to Early Jurassic Gardnerville Formation originally contained tuffaceous sedimentary rocks, thin-bedded limestones, siltstones, and argillites, but it was metamorphosed to hornfels at Pumpkin Hollow in proximity to the McLeod Hill Quartz Monzodiorite (Dilles and Proffett, 1995). The Ludwig Mine Formation includes a massive white to gray limestone at the base, a middle massive white gypsum horizon, and an upper quartzitic sandstone member and is latest Early Jurassic to middle Middle Jurassic in age (Proffett and Dilles, 2008). The Artesia Lake Volcanics consist of basaltic andesite lava flows and breccias near Ludwig but elsewhere include andesites and dacites. These volcanic rocks are interpreted to be the extrusive equivalents of the early units of the Yerington batholith (Proffett, 1969; Dilles, 1987; Proffett and Dilles, 1991, 2008). The overlying Fulstone Spring Volcanics are subaerial dacitic volcanic rocks that include lava flows, domes, breccias, and ignimbrites. The principal Mesozoic units that are present in the study area in the southern part of the Pumpkin Hollow deposit are the Mason Valley Limestone, the Gardnerville Formation, and the Ludwig Mine Formation (or Ludwig Limestone, e.g., Proffett and Dilles, 1984). The carbonate rocks also are commonly metamorphosed to marble or replaced by calc-silicate minerals, magnetite, and sulfides. Mesozoic strata are unconformably overlain by Tertiary volcanic and sedimentary rocks. The Tertiary stratigraphy of the Yerington district was defined by Proffett and Proffett (1976) and mostly consists of ash-flow tuffs and lavas, with lesser conglomerates. Many of the volcanic 7

10 units had no local eruptive sources. Subsequent work has revised the geochronology, suggested regional correlations of units, and identified possible eruptive sources (e.g., Deino, 1989; Dilles and Gans, 1995; Garside et al., 2002). The map of the Pumpkin Hollow area of Barrett and Dilles (1995) uses the designations of Proffett and Proffett (1976), and those designations continue to be used at the Pumpkin Hollow project and in this study. The most relevant units to this study are those that were deposited near the base of the Tertiary section. The lower part of the Tertiary section in the Yerington district contains early ignimbrites and conglomerates, but an additional, enigmatic breccia unit that has not been described elsewhere in the district has been tentatively identified at the base of the Tertiary section at Pumpkin Hollow. The breccia, for which the term karst sometimes has been applied in the field, contains clasts of brecciated white marble with rare to abundant clasts of granodiorite porphyry. Clasts are commonly angular but locally rounded (Fig. 3). The matrix of this unit is marble as well. The cement is most likely calcite, but is indistinguishable from the marble clasts and matrix. The enigmatic breccia unit is overlain by Tertiary basalts and conglomerates, including a conglomerate with dark basaltic clasts and a lighter colored conglomerate containing clasts of Mesozoic rock (Proffett and Proffett, 1976). The clasts of Mesozoic limestone can be large and have been confused in places with intact Mesozoic limestones (Fig. 4). The conglomerates in turn are overlain by the early ignimbrites (Proffett and Proffett, 1976). The basal units are unconformably overlain by the first thick, widespread, Tertiary ashflow tuff in the stratigraphy of the Yerington district, the Guild Mine member of the Mickey Pass Tuff, which corresponds to units T 2, T 1, and T 1v of Proffett and Proffett (1976). This unit has a 40 Ar/ 39 Ar age of 27.1 Ma (McIntosh et al., 1992). At Pumpkin Hollow, T 2 tends to be rich in lithic and pumice fragments and is moderately welded. T 1 is most easily distinguished from T 2 8

11 by its strongly welded nature and the presence of fiamme, and T 1v is the basal vitrophyre. There are several other members of the Mickey Pass Tuff. The Mickey Pass Tuff in turn is overlain by the Singatse Tuff and a series of tuffs that were mapped in the Yerington district as the Bluestone Mine Tuff. The Bluestone Mine Tuff is overlain by the Hu-Pwi Rhyodacite and is cut by andesites dikes. All of these units are older than 22 Ma. Following a hiatus of about 7 m.y., magmatism resumed with eruption of andesites and dacites of Lincoln Flat from ~15 Ma to ~13 Ma, which is about the time that normal faulting began in the Yerington district. The Wassuk Group, which is dated at ~11 to ~8 Ma in the Yerington district, consists primarily of conglomerates with interbedded sandstones and mudstones with basaltic andesite lavas. Finally, late Tertiary to Quaternary alluvium fills the modern half grabens. Intrusive rocks The Middle Jurassic Yerington batholith intruded a series of Triassic to Jurassic volcanic and sedimentary rocks, including limestones and argillites (Dilles, 1987). Three major intrusions are recognized within the composite Yerington batholith, which had a diameter of about 15 km and a volume of 1000 km 3 (Dilles and Proffett, 1995). The first, and largest, is the McLeod Hill Quartz Monzodiorite, dated at Ma (Dilles and Wright, 1988). Its intrusion was followed by emplacement of the Bear Quartz Monzonite, which was intruded into the center of the McLeod Hill Quartz Monzodiorite. Finally, the smallest of the three intrusions is the Luhr Hill Granite, which was emplaced into the core of the batholith. At least three cupolas formed near the top of the Luhr Hill Granite, and these cupolas were cut by granite porphyry dike swarms dated at Ma (Dilles and Wright, 1988). The granite porphyry dikes of the Luhr Hill Granite are responsible for the porphyry related-mineralization in the Yerington district (Dilles, 9

12 1987; Dilles and Proffett, 1995). The McLeod Hill Quartz Monzodiorite is present at Pumpkin Hollow, whereas granite porphyry dikes are sparse and only weakly altered to chlorite ± epidote (Dilles and Proffett, 1995). Dikes and sills of hornblende granodiorite porphyry of Proffett and Dilles (1984) were emplaced at ~165 Ma, mostly along Jurassic faults. Structural setting The Mesozoic metavolcanic and metasedimentary rocks in the Yerington district formed near the western edge of the North American continent and west of the major Mesozoic thrust belts (Proffett and Dilles, 2008). The exposures of these rocks in the McConnell Canyon area of the Singatse Range form a west-plunging anticline. Folding and metamorphism of those strata are interpreted to have occurred during emplacement of the Mesozoic batholiths (Proffett, 1969; Einaudi, 1977; Dilles and Proffett, 1995), and Mesozoic strata in the Pumpkin Hollow area are similarly deformed. The Yerington batholith is bounded by faults on its north and south sides by faults that drop the batholith 2.5 to 4 km (Dilles and Proffett, 1995), which may have contributed to preserving the porphyry systems from erosion. Mesozoic strata and Oligocene and Miocene volcanic rocks in the Yerington district generally dip E. The Oligocene-Miocene ash-flow tuffs are conformable to disconformable with one another, and the sequence is not broken by any major faults (Proffett and Proffett, 1976; Proffett, 1977). Steeper dips of Jurassic volcanic rocks compared to the oldest Tertiary volcanic rocks, however, indicate that rocks in the district may have been tilted as much as 15 between emplacement of the Shamrock batholith at 165 Ma and deposition of the oldest Oligocene tuffs (Dilles and Proffett, 1995), as is consistent with paleomagnetic data (Geissman 10

13 et al., 1982). The Yerington district has been extended >150% since deposition of the sequence of ash-flow tuffs by movement on three sets of north-south striking normal faults. The faults formed in three successive generations since 15 Ma, and the faults in each of these sets initially dipped moderately to steeply east (Proffett, 1977; Proffett and Dilles, 1984; Dilles and Gans, 1995). The normal faults are spoon shaped, with the concave surface facing to the east; the faults penetrated to depths of >8 km; and they have a slightly listric geometry in the down-dip direction, flattening ~0.3 to 0.7 /100 m (Proffett, 1977; Proffett and Dilles, 1984). Faults in the first and oldest of these sets (e.g., Singatse fault) currently dip gently east or are slightly overturned to the west, except near the sides of the spoons; surface dip measurements in their up-dip portions generally are ~10-25 E. Faults in the second set (e.g., May Queen) do not crop out in many places, but cross sections constrained by drill holes indicate that they currently dip moderately east at ~30. Faults in the third and youngest set (e.g., Range Front fault on the eastern side of the Singatse Range) currently dip fairly steeply east, with surface measurements of Geochronologic and thermochronologic constraints indicate that Tertiary normal faulting in the Yerington district and Wassuk Range occurred during three time periods. The first stage, associated with movement on the first set of faults, was between ~13.8 and 12.6 Ma. The second set of faults, whose ages of movement are less well constrained but range between 11 Ma and 8 Ma, produced only ~2-5 of westward tilting and 5% east-west extension in the Yerington district, although oblique-slip faults in the Wassuk Range produced greater amounts of slip and extension (Dilles and Gans, 1995). The third set of faults bound the modern basins and ranges (Proffett, 1977; Dilles and Gans, 1995), and this set of faults has major displacement and has 11

14 been active from 4 Ma to present, based on apatite fission track and (U-Th)/He thermochronology (Stockli et al., 2002; Surpless et al., 2002). Pumpkin Hollow deposit The Pumpkin Hollow (Lyon) deposit consists of five main ore bodies: E-2, East, North, South, and Southeast (Ohlin, 2010). The two ore bodies on the southern part of the property, South and Southeast, are of interest in this study. The various ore bodies in part may represent originally separate areas of mineralization, but some of the ore bodies clearly are separated by post-ore, Tertiary normal faults that may have variably dismembered one or more originally contiguous ore bodies. The main ore mineral at Pumpkin Hollow is chalcopyrite, but there is also minor bornite (Ohlin, 2010; French, 2010). Other sulfides include pyrite and lesser pyrrhotite. Strong correlation of Cu, Ag, and Au geochemical analyses suggest that the precious metals occur in chalcopyrite (Ohlin, 2010). There are two main types of ore bodies, which are differentiated by their host rocks (Matlock and Ohlin, 1996; Ohlin, 2010). The first type, exemplified by the North ore body, is a brecciated skarn body hosted by hornfels of in the Gardnerville Formation. This ore body is copper rich but magnetite poor, but the roots of this body are a copper-poor magnetite body. There were several stages of sulfide-magnetite-calc-silicate deposition. Calcite and quartz veins with chlorite, talc, and garnet are late-stage alteration minerals. The other four main ore bodies (South, Southeast, East, and E-2) are hosted by the Mason Valley Limestone (Ohlin, 2010). These ore bodies are magnetite rich, and the highest copper 12

15 grades occur in portions of the magnetite skarn. The South ore body consists of two main zones, a lower zone present in the footwall that has lower grades of copper (but higher grades of magnetite) than a zone found in the hanging wall, which has higher copper but lower magnetite grades. The Southeast ore body is similar to the South ore body. The East ore body consists of several magnetite- and chalcopyrite-rich lenses that occur at the boundary between sills of granodiorite and the Mason Valley Limestone. Finally, the E-2 ore body is similar to the East ore body, and it also is rich in magnetite and contains chalcopyrite at a boundary between granodiorite endoskarn and the Mason Valley Limestone. Methods Field methods Approximately three months were spent on the property. Field work consisted of core log analysis, field mapping, and three weeks of trench mapping. Core logs and access to land were provided by the Nevada Copper Corp. Collar coordinates and other information for the drill holes that were used in this study are contained in Appendix Table A1. Nearly 200 holes were used, four of which were oriented core holes (Rozelle, 2010). Core drilled by Nevada Copper Corporation has been logged and photographed, and holes drilled by them have reliable logs. The newest of these logs those from 2012, 2011, and the later logs from 2010 commonly record detail about the Tertiary units, which was utilized in this study. Pre-2010 logs do not often have detailed descriptions of Tertiary units. Older logs, such as those from the Anaconda era at Pumpkin Hollow, are generally reliable in their content, but the associated core commonly is no longer on the property. 13

16 Holes drilled and logged by US Steel in general are considered to be less reliable in content and are missing core. In both present and past core, many logs have long sections of missing core recorded. Core from many of the US Steel holes was later relogged by Anaconda geologists; in this case, both logs were utilized, as the US Steel logs for those holes tend to be more detailed but less accurate in their interpretation of rock type and alteration, whereas the Anaconda re-logs tend to be summaries with less detail but with rock types correctly identified. Structural analysis and reconstruction The structural analysis employed here uses fault surface maps, i.e., structure contour maps and geologic maps of hanging wall and footwall fault surfaces, to define the geometries of faults and the amount and direction of slip. This method is a three-dimensional technique, whereas the traditional, cross-sectional restoration technique is a two-dimensional method. Information is recorded on multiple layers, which may be either digital or physical (as in this case using colored pencils on multiple sheets of mylar, the results of which were ultimately drafted electronically). The method is summarized here, and details are provided in the appendix. In this study, the fault surface maps consist of four layers of information--one that shows all of the data and three that show interpretations and the constraints from a relevant subset of the data. The following four layers are generated for each fault: 1) the raw data, which includes the location and elevation of surface exposures and drill hole piercements and the lithology and alteration of rocks in the immediate hanging wall and footwall; 2) interpretive structure contours of the elevation data; 3) an interpretation of the rock type and alteration of the geology in the immediate hanging wall of the fault, and 4) an interpretation of the rock type and alteration of the 14

17 geology in the immediate footwall of the fault. The method makes it easier to project data properly in three dimensions and permits iterations between different possible interpretations to be explored while showing the locations of the data that constrain them. In this method, the geometry of the fault surface, including variations in strike and dip, is illustrated by Layer 2. The amount and direction of slip is determined by restoring the hanging wall block (Layer 3) in the up dip direction relative to the footwall (Layer 4), pinning geologic markers in the hanging wall to offset equivalents of the same markers in the footwall, permitting the amount and direction of slip to be measured or calculated. Depending on the geologic constraints available, there may be numerous possible solutions, or piercing points may be available that define a unique solution. The amount and direction of slip in general could vary along strike, and the method, in principle, permits display of an infinite number of slip vectors on the plane of the fault. Trench mapping In order to constrain the location and hanging wall/footwall lithologies of two post-ore faults for this study, Nevada Copper dug two exploratory trenches with a backhoe at the locations shown in Figure 4. The eastern trench refined the location of the Middle fault, although the fault is exposed only at the end of the trench. The western trench provided an excellent exposure of the Western fault. After the trenches were dug, the author cleaned out extraneous rock and talus, and then carefully cleaned the walls with paintbrushes. Paint markers were then applied every two ft (~.6 m) horizontally and vertically on both walls of each trench for reference. While mapping, the 15

18 walls were sprayed with water to stabilize the walls as well as to bring out the contrast in the different lithologies. The trench was mapped at a scale of 1 : 12 (1 in = 1 ft). The corners of these trenches were located on the map of Barrett and Dilles (1995) with GPS measurements. The trench maps are presented in Figure 5; a photomosaic of part of the Western trench (outlined in Fig. 5) is in Figure 6. Surface and Trench Mapping of the Western and Middle Faults In order to better constrain the location of the surface trace of the Western and Middle faults, key areas of the surface geologic map of the Pumpkin Hollow property (Barrett and Dilles, 1995) were remapped (Fig. 4). Afterward, Nevada Copper had two trenches excavated at locations where the faults were expected to be located in order to get exposures of the fault to make better structural observations and measurements. Western fault The first area to be remapped, shown in Figure 4, was straddles the Western fault. The unconformity between Mesozoic rocks and overlying Tertiary units is an important geologic marker for determining the amount of slip on the fault. At Point 1a of Figure 4 Jurassic granodiorite is overlain by Tertiary conglomerate. Point 1b indicates where a fault was reinterpreted to be located farther to the west due to the revisiting of the geology of an old prospect pit. This unit of the prospect pit is a continuation of the hornfels of the Gardnerville Formation. 16

19 Point 2 is the location of the trench dug out across the Western fault. This trench exposed the fault where it was previously mapped (Fig. 4). A small set of crystal fiber lineations has a trend and plunge of 205/23. This was the only place the author could find to measure orientation in the Western trench. This measurement does not reflect the slip orientation of the faulting, but the shear zone exposed by the trench indicated one measurement was not enough to orient the entire fault. Middle fault An area of the Middle fault is indicated in Figure 4 (Point 3d) was revisited because the Jurassic Ludwig Limestone crops out between two Tertiary units. This area is now interpreted as a large fragment of Ludwig Limestone in the conglomerate. The limestone here is weathered and rounded, as might be expected in the water-lain conglomerates. Figure 7 shows the rounded nature of the larger pieces of this limestone, as well as some of the very rounded cobbles that are scattered across this area. To the east, Point 4e was also revisited (Fig. 4) because of the complex map relationships. The unit originally mapped here as Ludwig Limestone also has characteristics of limestone clasts in a conglomerate. At point 4f where a north-south striking Tertiary vitrophyre unit was previously mapped, only outcrops of a Jurassic granodiorite porphyry dike were observed. To the northeast, Point 3g along the Middle fault was carefully examined for its triple junction intersections of contacts between Tertiary tuff, and Ludwig Limestone, and hornfels of the Gardnerville Formation. The limestone here is an in situ limestone. Several dip measurements on the Western fault range from 11 to 34. The location of the fault is farther to 17

20 the west than previously projected. Most of the trench is tuff, but the very western edge has limestone, with a small exposure of hornfels in the southwestern corner of the trench. The fault is not planar at the surface. It dips 31 on the southern wall of the trench and 22 on the north side. The strike of the fault is not perpendicular to the trench. Descriptions of the Normal Faults Each of the major faults in the southern part of the Pumpkin Hollow deposit is described in this section based on surface and drill hole observations. The collar coordinates, depths, and other characteristics of the drill holes used are provided in the Appendix. All drill and topographic data at the property are available in feet, rather than metric units. The faults in the area have two orientations, as shown in the cross section of Figure 8. Nearly flat faults are cut and offset by moderately east-dipping faults. The moderate dipping faults are described first. The main rock types observed are described in an earlier section, although the Mesozoic rocks exposed in drill holes at the deposit generally are strongly altered. The principal protoliths are the Mason Valley Limestone, the Gardnerville Formation, the Ludwig Limestone, and granodiorite porphyry. The Mason Valley Limestone is altered to marble, skarn (i.e., magnetitepoor skarn), and magnetite skarn (skarn with greater than or equal to 10 vol % magnetite content; H. Ohlin, pers. comm., The Gardnerville Formation was metamorphosed to hornfels and variably altered but less commonly has lenses of marble after thin limestone interbeds (Proffett and Dilles, 2008). The Ludwig Limestone can also be present as marble or be replaced by skarn, although the skarns observed in this study were mostly after the Mason Valley Limestone. 18

21 Finally, the granodiorite porphyries commonly are altered to endoskarn. The units shown on the fault surface maps are labeled by their altered equivalents. Western fault The Western fault is located on the western side of Pumpkin Hollow Its surface expression is about 4000 ft (~1220 m) long a NNE-SSW strike and has a mapped dip of 40 E (Barrett and Dilles, 1995). It is well exposed for ~1200 ft (~365 m) (including the western trench). About 35 drill holes were used in analyzing the location and depth of the fault. The characteristics of the Western fault in drill core range from thick sections of breccia and gouge (20 or more ft; 6+ m) to an abrupt change in lithology with little gouge evident. In rock chips from reverse circulation (RC) drilling, the fault is usually observed by a change in lithology over 5 or 10 ft (1.5 3 m). The shape of this fault as interpreted through drill holes appears to change little from its surface expression to at least a depth of about 300 ft below the surface expression (Fig. 9). Farther to the east, a flat fault is intersected in the hanging wall of the Western fault. Few drill holes that pierce the flat faults are deep enough to also pierce the continuation of the Western fault at depth, so the shape of the fault below the 4500 ft (~1370 m) contour is unknown. Where the geometry of the fault is well constrained, the structure contours (Fig. 9) indicate an average dip of ~30 E. A large portion of the stratigraphic sequence (Fig. 2) is exposed at the surface in the footwall of the Western fault (Barrett and Dilles, 1995) because Mesozoic and Tertiary units dip moderately to steeply westward and generally strike oblique to the strike of the Western fault. The Mesozoic rocks present in the footwall consist of altered equivalents of the Jurassic 19

22 granodiorite porphyries, the Ludwig Limestone, the Gardnerville Formation, and the Mason Valley Limestone (Fig. 10). The hanging wall of the Western fault has only the Tertiary volcanic units, beneath which is a subhorizontal fault (Fig. 8). Middle fault The Middle Fault lies about ft (~ m) east of the Western Fault. The Middle fault persists about 6200 ft (~1900 m) along strike in a northwesterly direction at the surface, although it is well exposed for only about 800 ft (~245 m) of strike length, including at the second trench. This study uses the southern 4800 ft (~1450 m) of the surface expression of the fault. Two dip measurements from Barrett and Dilles (1995) along fault are 11 and 30 E, about 140 ft (~40 m) apart. The Middle Fault itself is poorly constrained by these drill holes, with only two definitively recording the fault. Three shallowly dipping faults are cut and offset by the Middle fault and preserved in the hanging wall of the Middle fault. Two of these shallower faults are the Upper Middle Flat and Middle Flat faults. The Upper Middle Flat fault is presently above the Middle Flat fault. They are both observed in the drill holes in the northern part of the Middle fault s surface expression. They dip to the northwest, and are not continuous along strike of the Middle fault. The third, the Lower Middle Flat fault, is another shallowly dipping crosscut fault is further to the south along the trace of the Middle fault s surface expression. This Lower Middle Flat fault can be seen in Figure 8, but has fewer drill holes to constrain its geometry. The footwall of the Middle fault is the hanging wall of the Western fault (Fig. 8). The hanging wall has Tertiary volcanic rocks, including the vitrophyre, but no conglomerate (Fig. 9). 20

23 Below the vitrophyre are Mesozoic units, including Jurassic granodiorite porphyry, Gardnerville Formation, and skarn and magnetite skarn after the Mason Valley Limestone (Fig. 9). Western Flat fault The Western Flat fault is crosscut by the younger Western fault and is preserved in the hanging wall of the Western fault at a depth of about ft (~ m). The Western Flat fault is pierced by about 90 drill holes. It is subhorizontal (Fig. 10), with only ft (~30-60 m) of elevation difference over a 2000 ft (~600 m) distance for an overall gradient of about 4. The Western Flat fault has been eroded in the footwall of the Western fault. In the hanging wall of the Western fault, a section of Tertiary volcanic rocks and conglomerate unconformably overlies hornfels of the Gardnerville Formation and skarn after Mason Valley Limestone. The footwall contains only skarns of the Mason Valley Limestone (Fig. 10). Upper Middle Flat fault The Upper Middle Flat fault is the higher of the two faults of the older generation present in the hanging wall of the northern part of the Middle Fault (Fig. 11). These faults are not as flat as the Western Flat fault but appear to be more shallowly dipping than, and crosscut by, the younger Middle fault (Fig. 11). The Upper Middle Flat fault is exposed in about 35 drill holes, a relatively small data set but one large enough to indicate the presence of another fault below, the Middle Flat fault. The Upper Middle Flat fault dips about 27 NE (Fig. 11). The thickness of fault zones (gouge and breccia) ranges from about 5 to 30 ft (~2-10 m). The truncation of the Upper Middle Flat fault by the Middle fault occurs at elevations ranging from 4300 to 4500 ft 21

24 (~ m) (Fig. 11). The hanging wall of the Upper Middle Flat fault contains a sequence of Tertiary units, mostly Tertiary tuff but also small sections of the karst unit and Tertiary conglomerate. In the footwall is a Mesozoic sequence of magnetite skarn surrounded by skarn and granodiorite porphyry, with some andesite (Fig. 11). Middle Flat fault The Middle Flat fault is the lower shallowly dipping fault present in fault surface maps to the northern part of the Middle fault. It is also known from ~25 drill holes. The same drill holes penetrate the Middle Flat and Upper Middle Flat faults, but the projection of the Middle fault to depth is deeper than the bottom of most drill holes in this area. The contours are more irregular, but the average dip of the Middle Flat fault is ~23 NE (Fig. 12). Fault zones of the gouge and breccia can range from about 5 to 30 ft (2-10 m). This fault intersects the Middle fault between 4200 and 4400 ft (~ m) elevation. Both the hanging wall and footwall of the Middle Flat fault have a skarn sequence of a magnetite skarn core surrounded by skarn and endoskarn. Lower Middle Flat fault The Lower Middle Flat fault is observed in only a few drill holes and is best exposed in NC08-44 and USS-7. Its shape is less well known, but in Figure 8A it shown as a flat fault. The hanging wall of the LMF fault is also the hanging wall of the Middle fault; the footwall is poorly known but may have skarn and possibly limestone (according to the two drill holes). Other lithologies present are primarily based on predictions from the reconstruction (see below). 22

25 Interpretations Origin of the brecciated marble The Tertiary marble breccia is a new lithologic unit discovered at Pumpkin Hollow by Nevada Copper geologists. The field term karst has been applied to this unit, though a cavelike dissolution origin is questionable. This breccia appears directly over the Upper Middle Flat fault and could have several origins. This study reviews certain major breccia types that could be applicable to the Pumpkin Hollow breccias as a basis for analysis of the possible origin. An igneous breccia, defined here as a unit shattered and then cemented. This karst deposit, however, is not an igneous breccia, as the matrix is comminuted marble although Jurassic granodiorite porphyry can occur as clasts in the breccia. A hydrothermal breccia (Davies et al., 2008a, 2008b) is another breccia type common to the Yerington district and Pumpkin Hollow (Ohlin, 2010). A hydrothermal breccia is a breccia formed by hydrothermal processes and that is cemented by hydrothermal minerals. However, there is no alteration of the clasts within the breccia, which is common for hydrothermal breccias at Pumpkin Hollow. A tectonic breccia is another potential origin for the karst. In this case, the karst would be the breccia caused by the formation of one of the normal faults. If this were the case, the clasts of the breccia would be pieces of the hanging and footwall lithologies and would be present between the two fault blocks. This breccia does not appear to occur along a fault; instead, the karst is only present in the hanging wall of the Upper Middle Flat fault. 23

26 Rock avalanche breccias are another type of breccia that could be associated with the karst deposit. This type of breccia is caused by the uplift of the hanging wall or footwall of a fault. These fault blocks can become oversteepened to the point of slope failure and cause a landslide breccia (Dickinson, 1991; Krieger, 1977; Burchfiel, 1966). The source of the breccia can be in either the hanging wall or footwall of the fault in an actively forming half graben (Schmidt, 1971; Krieger, 1977), as illustrated by Dickinson (1991, Fig. 28). In either case, the matrix of rock avalanche breccias is formed principally by comminution of the breccia clasts. Although the matrix of the breccia unit at Pumpkin Hollow (mainly comminuted marble) is consistent with this origin, the stratigraphic position of the breccias unit is an apparent problem. Though the karst appears to be a stratigraphic unit that rests on the Tertiary unconformity and locally occurs at the base of the Tertiary section (Fig. 2), all of the known normal faulting occurs about the time of deposition of the Lincoln Flat andesite, after deposition of the entire sequence of ash-flow tuffs. In addition, no clear sources for the breccia have yet been identified. The stratigraphic position of the breccia unit at the Tertiary-Jurassic unconformity (Fig. 2) may be consistent with an origin related to near-surface dissolution, but the origin of the unit remains uncertain and deserves further study. Constraints on the amount and direction of slip on faults from reconstruction and fault surface maps To calculate slip vectors along faults, the distribution of lithologies in the hanging wall and footwall of a fault must be studied in detail, and fault surface maps are the visual product of such work. Professor Eric Seedorff has perfected this methodology using data from the 24

27 Robinson Mine in Ely, Nevada. Matching geologic markers in the hanging wall with corresponding equivalents in the footwall can constrain the net direction and amount of slip on a fault. Markers that define a line, which when cut by a fault plane produces a point on either side of the fault surface, constitute a piercing point, which uniquely defines the slip (e.g., Twiss and Moores, 1991, p. 60; Davis et al., 2012, p. 757). Offset of distinctive planar geologic markers on either side of the fault (e.g., a stratigraphic contact), which when cut by a fault plane produces a line on either side of the fault surface, provide useful information but require additional constraints or assumptions to define the amount and direction of slip. In the southern part of the Pumpkin Hollow deposit, there are too few drill holes to be able to track something as small as a dike across the deposits. Instead, the best geologic markers are the map-scale patterns of the lithologies, including altered equivalents. The displacement of a large zone of magnetite-rich replacement of limestone (which are the ore bodies) can be viewed as more diffuse piercing points. The unconformity between the Tertiary and underlying Triassic units is a geologic marker that is readily apparent in core logs and surface exposures, yet it constitutes a line, rather than a point, on either side of the fault. The estimates of direction and amount of slip for faults from this study are based on the fault surface maps (Figs. 9, 10, 11, 12), including data from the surface geologic maps (Fig. 4). In addition, a two-dimensional, cross-sectional reconstruction also is offered. The cross section has six drill holes that are within about 100 ft (~30 m) of the line of section. The reconstruction first restores the younger set of moderately dipping faults, then the earlier, subhorizontal set of faults (Fig. 8). Western fault 25

28 The Western fault has tight constraint on its slip direction and amount of slip because it has the drill holes piercing it in a cluster towards the southern part of its surface expression, consisting of about 30 holes. From these drill holes, a structural contour map was created (Fig. 9), and a dip for the fault could be calculated (about 30 ) down to a depth of about 4500 ft (~1370 m). A dip of 30 marks this fault as belonging to the later generation of faults on the Pumpkin Hollow property, and thus the first set to be reconstructed. The slip direction of this fault was interpreted to be S78 E on the basis of a geologic marker, the Tertiary/Jurassic unconformity as present in the hanging wall fault map and surface map. A true piercing point does not exist in this fault for the footwall of this fault has been exposed and eroded. However, other pieces of evidence may be used to help determine the approximate amount and direction of slip. Surpless (2010, 2012) mapped similar structures to the west. Proffett (1977) and Proffett and Dilles (1984) also mapped similar structures to the east in the Yerington district. The cross section and subsequent reconstruction of the South and Southeast ore bodies lies in the plane of this slip direction (Fig. 9). The reconstruction matched a Tertiary tuff and vitrophyre sequence observed in drill hole L-81 in the footwall of the Western fault to tuffs exposed in the hanging wall of the Western fault, as well as a skarn and magnetite skarn sequence found in the hanging wall and footwall. Along this fault there is 800 ft (~240 m) of slip. Middle fault The Middle fault has fewer constraints on its geometry, and so interpretations are based on two drill holes and surface data. When reconstructed as shown in Fig. 8, slip is about 950 ft (~290 m) along the fault. The reconstruction shows that the Lower Middle Flat fault in the hanging wall of the Middle fault is the continuation of the Western Flat fault (Fig. 8C). 26

29 Western Flat fault and Lower Middle Flat fault Once the movement on the younger generation of moderately dipping faults has been restored and untilted, it is apparent that the Western Flat and Lower Middle Flat faults are segments of the same fault of the earlier generation of flat faults at Pumpkin Hollow. The movement on the flat faults can then be restored and untilted until the original, pre-fault geology becomes clearer. The entire Tertiary and Mesozoic sequence in the South and Southeast deposits is present, from the Tertiary tuffs down to the Triassic Mason Valley Limestone (altered to skarns). This fault accommodated about 1950 ft (~600 m) of slip, originally on a steep fault but on segments of a fault that are now horizontal (Fig. 8). Altogether, the two generations of faults have accommodated about 3600 ft (~1100 m) of slip. If the first generation of faults originally had the same dip as the current generation, about 30 of tilting must have occurred along the second generation of faults to make the faults that are now flat as they are today. The Upper Middle Flat and Middle Flat faults are not present in the cross-sectional reconstruction but were tracked on fault surface maps. Upper Middle Flat fault Geological markers were used to connect points of similar boundary outlines to the magnetite body/skarn. Three such markers were picked to restore the Upper Middle Flat fault footwall to the Lower Middle Flat fault hanging wall (Fig. 11). Of these three markers, the two westernmost points do not appear to cross any of the interpreted structure contours, and so these 27

30 vectors are essentially horizontal. The westernmost vector is calculated to be 560 ft (~170 m) along a strike of N16 W. The middle vector is calculated to be 440 ft (~135 m) along the N20 W vector. Lastly, the easternmost vector is not horizontal. The horizontal distance is 340 ft (~100 m), but with a dip of 27, the calculated slip vector would be 354 ft of slip along a strike of N30 E. Lower Middle Flat Fault A similar set of geological markers was used to reconstruct the footwall of the Upper Middle Flat fault to the hanging wall of the Lower Middle Flat fault. Two markers were chosen. The first has a calculated slip of about 215 ft (~65 m) of slip in a direction of N44 E. The second set of piercing points results in a slip calculated to be about 269 ft (~80 m) in a direction of N65 E. Estimate of total extension at Pumpkin Hollow The estimate of the total extension across the South and Southeast ore bodies at Pumpkin Hollow is about 1800 feet (~550 m) of slip across the Western, Middle, Western-Lower Middle Flat faults. This was determined from the reconstruction in Fig. 8 by measuring the amount of slip on each fault once reconstructed. The slip, in turn, is determined by reconstructing the faults such that changes in lithologies match once the faults have been unfaulted. Tthe amount of extension at Pumpkin Hollow is about 200%. Discussion Relationship to normal faulting in the greater Yerington area 28

31 The Yerington district is an excellent example of an area that was highly extended by multiple generations of normal faults (Proffett, 1977; Proffett and Dilles, 1984; Dilles and Gans, 1995), and the map of the district recently has been enlarged to the east and south (Surpless, 2010, 2012). The first generation of normal faults, which includes the Singatse fault, has the shallowest dips (0-10 E). This set of faults accommodated the greatest amount of strain, and single faults accommodated as much as 4 km of slip. The second generation of faults includes the May Queen fault, dips E, and cuts the earlier generation of faults. The third and youngest generation of faults that bound the modern basins and ranges, including the Montana- Yerington, Sales, and Range Front faults, dips about E. Surpless (2012) documents a shift in the extension direction from ENE-WSW when faults of the first set were moving to WNW- ESE for the third set. The total extension in the Yerington district is >150% (Dilles and Gans, 1995), and adjoining areas of the Wassuk Range have been extended >200% (Surpless, 2012). The first generation of faults in the greater Yerington area corresponds to the early, subhorizontal faults described here in the Pumpkin Hollow area, such as the Western Flat, Upper Middle Flat, Middle Flat, and Lower Middle Flat faults, which do not crop out at Pumpkin Hollow but that are intersected by drill holes. The flat fault with the greatest amount of slip is the Western Flat-Lower Middle Flat fault, which has an estimated slip direction of S78 E. The younger generation of faults at Pumpkin Hollow, including the Western and Middle faults and another fault mapped farther to the east by Barrett and Dilles (1995), dip about 30-40, and these are correlated with the second generation of faults observed in the greater Yerington area. This generation of faults has ~900 ft (~275 m) of slip on each fault. Analogues have been recognized in the southern part of the Pumpkin Hollow deposit of the third generation of faults that are documented elsewhere in the region. The two-dimensional reconstruction of faults at 29

32 Pumpkin Hollow indicates ~200% extension, which is comparable to other estimates in the region. The high degree of complexity of faulting in the Pumpkin Hollow area is apparent because of the extensive drilling that has been required to develop the Pumpkin Hollow iron oxide-copper gold deposit. The present level of understanding of the structural geology of the deposit can contribute to plans for further exploration and development, but further refinements in understanding await additional exposure from future drilling and mining. Implications for displacement of orebodies Understanding of the post-ore structure of the district contributed to the discovery of the Ann-Mason deposit (Dilles and Proffett, 1995); it drove much of Anaconda s exploration in the district (Proffett, 1977); and it continues to be important in ongoing exploration of the district (e.g., Quaterra Alaska, 2010). Although there are multiple centers of porphyry mineralization in the district focused on different cupolas on the Luhr Hill Granite phase of the Yerington batholith (Dilles et al., 2000), some of the porphyry ore bodies are fault-bound fragments of larger, once-contiguous systems (Proffett and Dilles, 1995), and the same might be expected for ore bodies of the IOCG type such as Pumpkin Hollow. The relationship between the South and Southeast ore bodies in the southern part of the Pumpkin Hollow area can be addressed by combining the structural data collected in this study with alteration data previously collected by Nevada Copper geologists. The South and Southeast deposits are about 1.1 km apart in the direction of slip as measured in this study. The magnetite body that is the host of the Southeast ore body is in the footwall of the Middle fault, whereas the magnetite body that is the ore-bearing unit in the South deposit is in the hanging wall of that 30

33 fault. Restoration of movement on all faults considered in this study restores the Southeast ore body adjacent to the South ore body. Future work could extend structural studies further east to focus on the easternmost fault on the Pumpkin Hollow property, which appears to have a similar dip as the second generation of faults (30-40 ), and it crosscuts the same set of flat faults present in the hanging walls of the Western and Middle faults. Conclusions This study used fault surface map restorations and a cross-sectional reconstruction to constrain the timing, geometry, slip direction and amount of slip observed on the faults in the Southeast and South ore bodies of the Pumpkin Hollow deposit. Two generations of faults, an older one that is now subhorizontal and a younger one that has moderate (30-40 ) easterly dips, dismembered and tilted the deposit. These faults separated the once-contiguous South and Southeast deposits by about 1.1 km and extended the deposit by ~200%. Acknowledgments This study was supported by the Nevada Copper Corporation, a Hugh E. McKinstry Student Research Award from the Society of Economic Geologists, and Science Foundation Arizona. I would like to thank Mark Barton, Hank Ohlin, Greg French, Jacqueline Holmgren, Govi Hines, and George Davis for their thoughtful discussions, reviews, and expertise on the Pumpkin Hollow property throughout this study. Additional thanks goes to fellow student 31

34 Simone Runyon for additional discussions on the petrography of altered rocks in the Yerington district. References Armstrong, R.L., 1972, Low-angle (denudation) faults, hinterland of the Sevier Orogenic Belt, eastern Nevada and western Utah: Geological Society of America Bulletin, v. 83, p Barrett, L.F., and Dilles, J.H., 1995, Geologic map of the Pumpkin Hollow area, Yerington district, Nevada: Unpublished geologic map commissioned by Cyprus Amax Minerals Company, date uncertain (~1995), scale 1:6000. Barton, M.D., and Johnson, D.A., 1996, Evaporitic-source model for igneous-related Fe oxide- (REE-Cu-Au-U) mineralization: Geology, v. 24, p Barton, M.D., and Johnson, D.A., 2000, Alternative brine sources for Fe-oxide(-Cu-Au) systems: Implications for hydrothermal alteration and metals, in Porter, T.M., ed., Hydrothermal iron oxide copper-gold and related deposits--a global perspective: Glenside, South Australia, Australian Mineral Foundation, p Barton, M.D., Girardi, J.D., Kreiner, D.C., Seedorff, E., Zurcher, L., Dilles, J.H., Haxel, G.B., and Johnson, D.A., 2011, Jurassic igneous-related metallogeny of southwestern North America, in Steininger, R.C., and Pennell, W.M., eds., Great Basin evolution and metallogeny: Geological Society of Nevada, Symposium, Reno/Sparks, May 2010, Proceedings, v. 1, p

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37 Dilles, J.H., and Proffett, J.M., Jr., 1995, Metallogenesis of the Yerington batholith, Nevada, in Pierce, F.W., and Bolm, J.G., eds., Porphyry Copper Deposits of the American Cordillera: Arizona Geological Digest 20, p Dilles, J.H., and Wright, J.E., 1988, The chronology of early Mesozoic arc magmatism in the Yerington district of western Nevada and its regional implications: Geological Society of America Bulletin, v.100, p Dilles, J.H., Farmer, G.L., and Field, C.W., 1995, Sodium-calcium alteration by non-magmatic saline fluids in porphyry copper deposits: Results from Yerington, Nevada, in Thompson, J.F.H., ed., Magmas, fluids, and ore deposits: Mineralogical Association of Canada Short Course, v. 23, p Dilles, J.H., Einaudi, M.T., Proffett, J.H., Jr., and Barton, M.D., 2000, Overview of the Yerington porphyry copper district: Magmatic to nonmagmatic sources of hydrothermal fluids: Their flow paths and alteration effects on rocks and Cu-Mo-Fe-Au ores, in Dilles, J.H., Barton, M.D., Johnson, D.A., Proffett, J.M., and Einaudi, M.T., eds., Part I. Contrasting styles of intrusion-associated hydrothermal systems: Society of Economic Geologists Guidebook Series, v. 32, p Einaudi, M.T., 1977, Petrogenesis of the copper bearing skarn at the Mason Valley mine, Yerington district, Nevada: Economic Geology, v. 72, p Einaudi, M.T., 2000, Field trip day three: Skarns of the Yerington district, Nevada: A triplog and commentary, in Dilles, J.H., Barton, M.D., Johnson, D.A., Proffett, J.M., Jr., and Einaudi, M.T., eds., Part I. Contrasting styles of intrusion-associated hydrothermal systems: Society of Economic Geologists Guidebook Series, v. 32, p

38 Einaudi, M.T., 2000, Field trip day three: Skarns of the Yerington district, Nevada: A triplog and commentary, in Dilles, J.H., Barton, M.D., Johnson, D.A., Proffett, J.M., Jr., and Einaudi, M.T., eds., Part I. Contrasting styles of intrusion-associated hydrothermal systems: Society of Economic Geologists Guidebook Series, v. 32, p French, G.M., ed., 2010, IOCG and porphyry-related deposits of western Nevada: Geological Society of Nevada Symposium 2010 Great Basin Evolution and Metallogeny, Field Trip Guidebook No. 7, 85 p. Gans, P.B., Miller, E.L., McCarthy, J., and Ouldcott, M.L., 1985, Tertiary extensional faulting and evolving ductile-brittle transition zones in the northern Snake Range and vicinity: new insights from seismic data: Geology, v. 13, p Garside, L.J., Henry, C.D., and Boden, D.R., 2002, Far-flung ash-flow tuffs of Yerington, western Nevada erupted from calderas in the Toquima Range, central Nevada [abs.]: Geological Society of America Abstracts with Programs, v. 34, no. 6, p. 44. Geissman, J.W., Van der Voo, R., and Howard, K.L., 1982, Paleomagnetic study of the structural deformation in the Yerington district, Nevada. 1. Tertiary units and their tectonism. 2. Mesozoic basement units and their total and pre-oligocene tectonism: American Journal of Science, v. 282, p Gibson, P.C., 1987, Geology of the Buckskin mine, Douglas County, Nevada: Unpublished M. S. thesis, University of Nevada, Reno, 93 p. Harris, N.B., and Einaudi, M.T., 1982, Skarn deposits in the Yerington district, Nevada Metasomatic skarn evolution near Ludwig: Economic Geology, v. 77, p

39 Heatwole, D.A., 1978, Controls of oxide copper mineralization, MacArthur property, Lyon County, Nevada, in Jenney, J.P., and Hauck, H.R., eds., Porphyry Copper Symposium, Arizona Geological Society and University of Arizona Symposium, Tucson, Arizona, March 1976, Proceedings: Arizona Geological Society Digest v. 11, p Krieger, M.H., 1977, Large landslides, composed of megabreccia, interbedded in Miocene basin deposits, southeastern Arizona: U.S. Geological Survey Professional Paper 1008, 25 p. Lipske, J.L., and Dilles, J.H., 2000, Advanced argillic and sericitic alteration in the subvolcanic environment of the Yerington porphyry copper system, Buckskin Range, Nevada, in Dilles, J.H., Barton, M.D., Johnson, D.A., Proffett, J.M., Jr., and Einaudi, M.T., eds., Part I. Contrasting styles of intrusion-associated hydrothermal systems: Society of Economic Geologists Guidebook Series, v. 32, p Matlock, J.A., and Ohlin, H.N., 1996, Lyon copper-iron skarn deposit, Yerington mining district, Lyon County, Nevada, in Green, S.M., and Struhsacker, E.M., eds., Geology and ore deposits of the American Cordillera: Geological Society of Nevada Field Trip Guidebook Compendium, 1995, Reno/Sparks, p McIntosh, W.C., Geissman, J.W., Chapin, C.E., Kunk, M.J., and Henry, C.D., 1992, Calibration of the latest Eocene-Oligocene geomagnetic polarity time scale using 40 Ar/ 39 Ar dated ignimbrites: Geology, v. 20, p McIntyre, J.L., 1990, Late Cenozoic structure of the central Wassuk Range, Mineral County, Nevada: Unpublished M. S. thesis, Corvallis, Oregon State University, 107 p. Ohlin, H.N., 2010, Geology of the Pumpkin Hollow deposits, Lyon County, Nevada, in French, G.M., ed., IOCG and porphyry-related deposits of western Nevada: Geological Society 37

40 of Nevada Symposium 2010 Great Basin Evolution and Metallogeny, Field Trip Guidebook No. 7, p Proffett, J.M., Jr., 1969, Report on the geology of the Yerington district: Laramie, Wyoming, American Heritage Museum, Anaconda Archives, 413 p. Proffett, J.M., Jr., 1977, Cenozoic geology of the Yerington district, Nevada, and implications for the nature and origin of Basin and Range faulting: Geological Society of America Bulletin, v. 88, p Proffett, J.M., Jr., and Dilles, J.H., 1984, Geologic map of the Yerington district, Nevada: Nevada Bureau of Mines and Geology Map 77, scale 1:24,000. Proffett, J.M., Jr., and Dilles, J.H., 1991, Middle Jurassic volcanic rocks of the Artesia Lake and Fulstone Springs sequences, Buckskin Range, Nevada, in Buffa, R., and Coyner, A.R., eds., Field Trip Guidebook Compendium, Geology and ore deposits of the Great Basin, Geological Society of Nevada, Symposium, Reno/Sparks, April 1990, Proceedings, v. 2, p Proffett, J.M., Jr., and Dilles, J.H., 2008, Lower Mesozoic sedimentary and volcanic rocks of the Yerington region, Nevada, and their regional context, in Wright, J.E., and Shervais, J.W., eds., Ophiolites, arcs, and batholiths: A tribute to Cliff Hopson: Geological Society of America Special Paper 438, p Proffett, J.M, Jr., and Proffett, B.H., 1976, Stratigraphy of the Tertiary ash-flow tuffs in Yerington district, Nevada: Nevada Bureau of Mines and Geology Report 27, 28 p. 38

41 Quaterra Alaska, Inc., 2010, MacArthur prospect, Yerington, Nevada, in French, G.M., ed., IOCG and porphyry-related deposits of western Nevada: Geological Society of Nevada Symposium 2010 Great Basin Evolution and Metallogeny, Field Trip Guidebook No. 7, p Reeves, R.G., Shawe, F.R., and Kral, V.E., 1958, Geologic map and sections of the Minnesota mine, in Iron ore deposits of Nevada: Nevada Bureau of Mines Bulletin 53, Part B, p Rozelle, J.W., 2010, NI Preliminary Economic Assessment Update, Pumpkin Hollow copper project, Lyon County, Nevada, United States, Prepared for Nevada Copper Corporation: Golden, Colorado, Tetra Tech, January 12, 2010, revised January 13, 2010, 248 p., Schmidt, E.A., 1971, A structural investigation of the northern Tortilla Mountains, Pinal County, Arizona: Unpublished Ph.D. thesis, Tucson, University of Arizona, 248 p. Sibson, R.H., 1977, Fault rocks and fault mechanisms: Journal of the Geological Society of London, v. 133, p Smith, M.R., 1984, The Pumpkin Hollow magnesian iron-copper skarn, in Johnson, J.L., ed., Exploration for ore deposits of the North American Cordillera: Association of Exploration Geochemists Field Trip Guidebook, 1984, Regional symposium, Reno, Field Trip 10, p

42 Stockli, D.F., Surpless, B.E., Dumitru, T.A., and Farley, K.A., 2002, Thermochronological constraints on the timing and magnitude of Miocene and Pliocene extension in the central Wassuk Range, western Nevada: Tectonics, v. 21(4), doi: /2001tc001295, 19 p. Surpless, B.E., 2010, Geologic map of the central Wassuk Range, western Nevada: Geological Society of America Map and Chart Series MCH-098, scale 1:24,000, text, 10 p. Surpless, B.E., 2012, Cenozoic tectonic evolution of the central Wassuk Range, western Nevada, USA: International Geology Review, v. 54, p Surpless, B.E., Stockli, D.F., Dumitru, T.A., and Miller, E.L., 2002, Two-phase westward encroachment of Basin and Range extension into the northern Sierra Nevada: Tectonics, v. 21(1), doi: /2000tc001257, 13 p. Twiss, R.J., and Moores, E.M., 1992, Structural geology: New York, W. H. Freeman and Company, 532 p. Wernicke, B.P., 2009, The detachment era ( ) and its role in revolutionizing continental tectonics, in Ring, U., and Wernicke, B. P., eds., Extending a continent: Architecture, rheology and heat budget: Geological Society of London Special Publication 321, p Wernicke, B., and Burchfiel, B.C., 1982, Modes of extensional tectonics: Journal of Structural Geology, v. 4, p Williams, P.J., Barton, M.D., Johnson, D.A., Fontboté, L., de Haller, A., Mark, G., Oliver, N. H.S., and Marschik, R., 2005, Iron oxide copper-gold deposits: Geology, space-time distribution, and possible modes of origin, in Hedenquist, J.W., Thompson, J.F.H., 40

43 Goldfarb, R.J., and Richards, J.P., eds., Economic Geology 100th Anniversary Volume, p

44 APPENDIX Drill Hole Information TABLE A1. Coordinates of Drill Holes Used in This Study Hole ID Area Y X Z Max Depth RC Depth Company GT10-05 SO NC GT10-06 SO NC GT10-08 SO NC GT10-11 SO NC L-1 SO US L-2 SO US L-4 SO US L-6 SE US L-11 SE US L-13 SO US L-14 SO US L-15 SO US L-15A SO US L-16 SO US L-17 SO US L-18 SO US L-19 SO US L-20 SO US L-20A SO US L-21 SO US L-22 SO US L-23 SO US L-24 SO US L-25 SO US L-26 SO US L-27 SO US L-30 SO US L-41 SO US L-42 SO US L-43 SE US L-45 SO US L-46 SO US L-47 SO US L-48 SO US 42

45 L-49 SO US L-50 SO US L-51 SO US L-53 SE US L-54 SE US L-57 SE US L-58 SE US L-62 SO US L-65 SE US L-66 SE US L-67 SO US L-68 SO US L-69 SO US L-70 SO US L-71 SO US L-72 SO US L-73 SO US L-74 SO US L-75 SO US L-82 SO US L-86 SO US L-87 SO US L-88 SO US L-90 SO US L-91 SO US L-94 SO US L-95 SO US L-99 SO US L-100 SO US L-101 SO US L-102 SO US L-103 SO US L-104 SO US L-105 SO US L-106 SO US L-107 SO US L-108 SO US L-109 SO US L-110 SO US L-111 SO US L-112 SO US L-113 SO US L-114 SO US 43

46 L-115 SO US L-116 SO US L-117 SO US L-118 SO US L-119 SO US L-120 SO US L-121 SO US L-122 SO US L-123 SO US L-126 SO US L-127 SO US L-129 SO US L-130 SO US L-138 SO US L-139 SO US L-140 SO US L-141 SO US L-142 SO US L-143 SO US L-144 SE US L-145 SE US L-146 SO US L-148 SO US L-156 NO US L-172 SE US L-173 SE US L-178 SO US L-185 NO US L-186 SoNO US L-187 SE US L-198 SE US L-201 SE US L-209 SO US MW10-01 SO NC NC07-30 SO NC NC07-33 SE NC NC08-10 SO NC NC08-11 SO NC NC08-16 SO NC NC08-17 SO NC NC08-19 SO NC NC08-21 SO NC NC08-23 SO NC 44

47 NC08-25 SO NC NC08-26 SO NC NC08-27 SE NC NC08-31 SO NC NC08-32 SE NC NC08-33 SO NC NC08-34 SO NC NC08-37 SE NC NC08-43 SE NC NC08-44 SE NC NC08-45 SO NC NC08-50 SO NC NC08-51 SE NC NC08-52 SO NC NC08-53 SO NC NC08-57 SO NC NC08-58 SO NC NC08-59 SO NC NC08-62 SO NC NC09-04 SO NC NC09-06 SO NC NC09-07 SO NC NC10-12 SO NC NC10-13 SO NC NC10-22 SO NC NC10-26 SO NC NC10-28 SO NC NC10-33 SO NC NC10-34 SO NC NC10-35 SO NC NC10-36 SO NC NC10-37 SO NC NC10-40 SO NC NC10-43 SO NC NC10-56 SO NC NC10-58 SO NC NC10-64 SO NC NC10-66 SE NC NC10-67 SE NC NC10-68 SE NC NC11-06 SO NC NC11-10 SO NC NC11-19 SO NC 45

48 NC11-23 SO NC NC11-24 SO NC NC11-28 SE NC NC11-31 SO NC NC11-32 SO NC NC11-40 SO NC NC11-45 SO NC NC11-49 SE NC NC11-52 SO NC NC12-02 SO NC NC12-04 SO NC NC12-06 SO NC NC12-07 SO NC NC12-10 SO NC S93-8 SO CY S93-9 SO CY S93-10 SO CY S93-11 SO CY USS-1 SoEA AN USS-2 SE AN USS-4 SE AN USS-5 SE AN USS-7 SE AN USS-10 SE AN USS-11 SE AN USS-12 SE AN USS-13 SE AN USS-16 SE AN USS-17 SE AN USS-19 SE AN USS-20 SE AN USS-25 NO AN USS-82 SO AN USS-85 NO AN USS-86 NO AN Abbreviations Areas: EA = East ore body; NO = North ore body; SE = Southeast ore body; SO = South ore body; So = South of (i.e., SoSE = South of the Southeast ore body) Companies: AN = Anaconda; CY = Cyprus; NC = Nevada Copper; US = US Steel Notes Depths are in feet; Coordinates for X and Y are for the Nevada State Plane West Grid Additional Information on Fault Surface Maps 46

49 The structural method employed here is a three-dimensional technique that uses fault surface maps, i.e., geologic maps of the fault surfaces. The method makes it easier to project data properly in three dimensions and permits iterations between different possible interpretations to be explored while showing the locations of data that constrain them. Information is recorded on multiple layers, which may be either digital or physical, to keep related interpretations and the relevant observational constraints. In this study, color-coded information was recorded with colored pencils on four layers on separate sheets of mylar, as described below, with a separate set of four sheets for each fault. Each sheet has a survey grid in order to compare it easily with the other layers and available geologic maps of the surface geology. Layer 1: Data The data layer contains the observational information for a given fault. The surface trace of the fault over its mapped length is shown, with strike and dip measurements of the fault, if available. The points where major elevation contours cross the fault are marked and labeled. Locations where each drill holes pierces the fault are marked (e.g., with a black dot) and labeled with four pieces of information for each hole: 1) the number of the drill hole (e.g., NC10-56), 2) the elevation of the fault in that drill hole, obtained from drill logs, and 3) the lithologies in the immediate hanging wall of the fault, and 4) the lithology in the immediate footwall of the fault. A useful practice that was utilized here is to also include drill holes that nearly pierced the fault. Layer 2: Structure contours The structure contour layer is constructed on a second sheet of mylar. Data relevant to the elevation of the fault are transferred from the data layer. An interpretation of the structure contours of the fault surface are drawn, constrained by elevations from drill holes and surface traces of the fault. Gaps and offsets in the contours result if the fault was cut and offset by a younger fault, creating gaps in the fault surface. Consequently, generation of a structural contour map for a fault may be an iterative process, as interpretations from one fault are reconciled with those of other faults. Layer 3: Geologic map of the hanging wall The geologic map of the hanging wall is made on third piece of mylar. By placing it over the data layer, the subset of data that are relevant to the geology of the hanging wall can be transferred to the sheet. The data include the geology of the rocks in the immediate hanging wall of the mapped surface traces of the fault and data from drill holes that pierce the fault, with some consideration given to holes that nearly reach the fault surface. Colors are assigned to the various lithologies. The contacts between different lithologies (unconformities, depositional, intrusive, or related to other faults) then are interpolated or extrapolated, marked with the appropriate symbols (e.g., wavy lines for unconformities). Such interpretations also are guided by other geologic constraints that may exist (e.g., thicknesses of various stratigraphic units). 47

50 Layer 4: Geologic map of the footwall The geologic map of the hanging wall is made on fourth sheet of mylar, using the same methodology as for Layer 3 but using data relevant to the geology of the immediate footwall of the fault. Use of the layers for palinspastic reconstructions The geometry of the fault surface, including variations in strike and dip, is illustrated by the structure contours of Layer 2 after gaps created by offsets by younger, crosscutting faults are closed. The amount and direction of slip is determined by restoring the hanging wall block (Layer 3) in the up dip direction relative to the footwall block (Layer 4), pinning geologic markers in the hanging wall to offset equivalents of the same markers in the footwall. This permits the amount and direction of slip to be measured or calculated. Depending on the geologic constraints available, there may be numerous possible solutions, or piercing points may be available that define a unique solution. The amount and direction of slip in general varies along strike, and the method, in principle, permits display of an infinite number of slip vectors on the plane of the fault. Independent constraints, such as bedding-to-fault angles of syntectonic strata, must be available to determine how each fault surface should be restored to its original dip. 48

51 Figure Captions Figure 1: Generalized geologic map of the study area modified from Dilles (1993). Inset, geographic map of Nevada with emphasis on the western region, including the Yerington district. Map shows the locations of the Wassuk and Singatse Ranges to the west of Yerington and the Walker Lane belt to the east. Major cities are labeled. Figure 2: Stratigraphic column for the South and Southeast ore bodies at the Pumpkin Hollow deposit. Figure 3: Karst or Tertiary marble breccia in drill core. Rock is HQ size core with diameter of 6.4 cm. Clasts can be fine-grained to porphyritic granodiorite or possibly andesite. Dark, monolithic clasts are Gardnerville Formation. Figure 4: Local revisions of the Barrett and Dilles (1995) map of the Pumpkin Hollow Property. Inset: Original map. Remapped areas are surrounded by numbered black boxes. Areas are: 1: a) Tertiary conglomerate remapped as Jurassic granodiorite porphyry (Jgdp); unit was most likely also covered by Tertiary conglomerate, as originally mapped, but most outcrops here are of Jgdp origin. B) Jgdp dike investigated and not observed to the extent as originally mapped. C) Small outcrop (prospect pit) originally mapped as a Tertiary tuff, now mapped hornfels of the Gardnerville Formation. 2: location of the western trench. 3: d) Several units originally mapped as Tertiary early ignimbrite, Ludwig limestone, and Tertiary conglomerate now all interpreted as Tertiary conglomerate. g) Location of eastern trench. 4: e) Unit of Ludwig limestone remapped as Tertiary conglomerate, as well as a unit previously mapped as Tertiary vitrophyre now interpreted as Jgdp dike. Figure 5: A) Trench maps from the Western trench at 1:12 scale. B) Trench maps from the Eastern trench at a 1:12 scale. Figure 6: Photomosaic of a portion of the Western trench. Note the sheared units. Mosaic is unscaled because pictures have been distorted to piece together; however, orange dots are 2 feet (~.6 m) apart horizontally and vertically in original trench. Figure 7: Intact and reworked limestones from the Pumpkin Hollow property. A) Unit previously mapped as intact Ludwig Limestone now interpreted to be reworked limestone within a Tertiary conglomerate. B) Fresh, intact Ludwig Limestone on the Pumpkin Hollow property, at point 3g indicated in Figure 4. Figure 8: A) Cross section of the Pumpkin Hollow deposit across the Western, Middle, Western Flat, and Lower Middle Flat faults. B) Reconstruction of the younger set of faults. C) Reconstruction of the older set of faults. Figure 9: Fault surface maps of the A) hanging wall and B) footwall of the Western Fault. 49

52 Figure 10: Fault surface maps of the A) hanging wall and B) footwall of the Western Flat fault. Figure 11: Fault surface maps of the A) hanging wall and B) footwall of the Upper Middle Flat fault. Figure 12: Fault surface maps of the A) hanging wall and B) footwall of the Middle Flat fault. 50

53 Figure 1 California Nevada Reno N 50 miles Winnemucca Elko Reno Carson City Yerington Tonopah Carson City Yerington Las Vegas Tonopah KEY Wassuk Range Singatse Range Walker Lane

54 Tertiary 11-8 Ma Early Tertiary Tertiary Oligocene Basal Tertiary Deposits Jurassic Triassic Thickness Column Description Unit Variable Recent poorly sorted volcanic sand and gravel. Alluvium Slight unconformity ~400 feet Conglomerates with interbedded sandstones and silty mudstones, locally arkosic. Wassuk Group Major unconformity Guild Mine Member T1v-T2 Mickey Pass Tuff Figure 2 Age Quaternary feet feet T2: Brownish, pink, lavender, gray or green, moderately welded, pumice and lithic-rich ash flow tuff containing sanidine, quartz, plagioclase, and biotite phenocrysts. T1: Brown, strongly welded, crystal- and fiame-rich ash flow tuff containing plagioclase, biotite, and pyroxene phenocrysts in the basal portion and grading upwards into sanidine, quartz, some plagioclase, and biotite phenocrysts near the top. 0 - feet feet feet T1v: Black, strongly welded basal vitrophyre of the T1 tuff. White, buff or reddish, weakly to moderately welded, ash flow tuffs that lay directly on the eroded early Tertiary surface or upon basal conglomerate (see below). They have been heavily eroded and are not always present. Dark brown to black basalt-andesite agglomerates and conglomerates. Yellow to buff conglomerates with Mesozoic volcanic and metavolcanic clasts. Interbedded and overlain by basalt-andesite conglomerates. Erosional unconformity Tertiary Early Ignimbrite Tertiary Conglomerates 0 - feet 150 feet White marble clastic unit with rare to abundant, fine-grained to porphyrytic granodiorite clasts, generally angular but locally rounded. Only locally present. Major angular unconformity White marble and/or blue-gray laminated limestones that are often brecciated in areas of skarning. Can have trace sphalerite, arsenopyrite, and molybdemnite. Tertiary Karst Deposit Ludwig Limestone feet Volcanic tuffs and siltstone interbedded with limestone. Possibly straddles the Triassic-Jurassic boundary. Locally hornfelsed and/or skarned. Gardnerville Formation 1200 feet Blue-black to white marble limestone. Locally skarned. Mason Valley Limestone

55 Figure inches

56 Eastern Fault Qal Quaternary Alluvium T1/T2 Tertiary Tuffs T1v Tertiary Basal Vitrophyre Tcg Tertiary Conglomerate Tei Tertiary Early Ignimbrite Tba Tertiary Basalt Jgdp Jurassic granodiorite porphyry Jl Ludwig Limestone TrJg Gardnerville Formation Trl Mason Valley Limestone N 1 b a 2 3 g d 4 f e Pumpkin Hollow Project Middle Fault Western Fault Figure 4 Lithologic contact Fault A A B

57 Figure 5A West Trench North Face KEY Alluvium Porphyry clast Tuff White ash Oxidized Tuff Clay Gouge Calcite Breccia Hornfels Limestone Trench boundaries Shear Zone Limy material Copper Oxide Faults West Trench South Face Alluvium/top of trench Bottom of trench Alluvium/top of trench Bottom of trench 2 feet 2 feet

58 Figure 5B East Trench North Face West Exposure East Trench South Face Alluvium/top of trench Bottom of trench Alluvium/top of trench Bottom of trench 175/44 070/75 2 feet 2 ft

59 Figure 6 West Trench South Face E W Tuff Limestone Hornfels Approx. 1 foot

60 Figure 7 A B