Geology Manual. Properties of Minerals & Rocks in the Kumaun Region. Compiled for CHIRAG

Transcription

1 Geology Manual Properties of Minerals & Rocks in the Kumaun Region Compiled for CHIRAG Prepared by: Sophia Yee B.Sc. Geology, M.Sc. Water Management Montreal, Quebec, Canada May 2013

2 SECTION 1: INTRODUCTION TO MINERALS & ROCKS 1.1 MINERALS Minerals are composed of elements that are found in the periodic table. There are numerous groups of minerals which are classified according to their chemical and physical properties. The main groups of minerals found in this region are as follows: Table 1. The main groups of minerals in the Kumaun region Mineral group Name Formula SILICATES Tectosilicates Quartz SiO 2 (Feldspar Family) Alkali Feldspar - Orthoclase Plagioclase Feldspar - Albite KAlSi 3 O 8 NaAlSi 3 O 8 Phyllosilicates/(Mica Group) Biotite K(Mg,Fe) 3 (AlSi 3 )O 10 (OH) 2 Muscovite KAl 2 (AlSi 3 )O 10 (OH) 2 Sericite - Talc/Soapstone Mg 3 Si 4 O 10 (OH) 2 Illite (K,H 3 O)(Al,Mg,Fe) 2 (Si,Al) 4 O 10 [(OH) 2 H 2 O (Chlorite Group) Chlorite (Mg,Fe) 3 (Si,Al) 4 O 10 (OH) 2 (Mg,Fe) 3 (OH) 6 Inosilicates (Amphibole Group) Hornblende (Ca.Na) 2-3(Mg,Fe,Al) 5 Si 6 (Al,Si) 2 O 22 (OH) 2 Carbonates/Evaporites Calcite CaCO 3 Gypsum CaSO 4 2H 2 O Limestone CaCO 3 Dolomite (CaMg)(CO 3 ) 2 2

3 1.2 ROCKS Rocks can be classified into three types: igneous, sedimentary and metamorphic. The simple schematic below represents the rock cycle (see Figure 1). Figure 1. A simplified representation of the rock cycle Igneous rocks are formed either on the Earth s surface (by the cooling of lava) or below the surface with the crystallization of magma. Sedimentary rocks are formed by depositional (transporting eroded particles) or evaporative processes in combination with lithification (consolidating different layers of particles). Metamorphic rocks are formed under diagenetic processes in which sedimentary rocks are buried and undergo changes in pressure and temperature. Depending on the magnitude of these changes, a different rock can be born. The specific classification of these rocks is done according to the graph of metamorphic facies (see Figure 2). Main facies: Low T and low P = Zeolite Moderate - high T and low P = Prehnite-Pumpellyite Low T - high P = Blueschist Moderate - high T and moderate P = Greenschist Amphibolite Granulite Moderate - high T and high P = Eclogite Figure 2. Metamorphic facies (see section 3 for a description of a metamorphic reaction) 3

4 Table 2. Common rocks within (or outside of) the Kumaun region Rock type Name Class IGNEOUS Basalt (w/ or w/o vesicles) Extrusive/Volcanic Granite Intrusive/Plutonic SEDIMENTARY Conglomerate/Breccia Clastic/fragmental Sandstone Clastic/fragmental Mudstone/Claystone/Siltstone Clastic/fragmental Shale Limestone Dolostone Clastic/fragmental Organic/bioclastic Crystalline METAMORPHIC Slate Low-grade Phyllite Schist Gneiss Quartzite Marble Mica Schist Green Schist Talc Schist Augen Gneiss Medium-grade High-grade 4

5 SECTION 2: PROPERTIES 2.1 MINERALS Minerals have various chemical properties which are determined by their elemental composition. However, only a domain of Geology, called mineralogy called Spectroscopy, can be used to identify such microscopic features. For the purpose of field identification, simple distinguishing features can be used: 1. Color: not a diagnostic characteristic 2. Hardness: The Mohs Scale of Hardness (see Table 3) is used to determine the relative hardness of a mineral compare to the known hardness of a mineral or a standard object. Table 3. The Mohs scale of Hardness Hardness Mineral Formula 1 Talc Mg 3 Si 4 O 10 (OH) 2 2 Gypsum CaSO 4 2H 2 O 3 Calcite CaCO 3 4 Fluorite CaF 2 5 Apatite Ca 5 (PO 4 ) 3 (OH-, Cl-, F-) 6 Feldspar (Orthoclase) KalSi 3 O 8 7 Quartz SiO 2 8 Topaz Al 2 SiO 4 (OH-, F-) 2 9 Corundum Al 2 O 3 10 Diamond C Three common objects hardness value for comparative purposes: Fingernail = 2.5 Coin = 3.0 Steel blade = Streak: the color a mineral gives off when rubbed against a surface (must be harder than its own hardness. 4. Cleavage: denotes the breaking pattern of a mineral along its regular surface (depending on its crystal/chemical structure). This occurs when a mineral is strained beyond its limits. A mineral that has cleavage surfaces (2 types: perfect or good) is contrasted to a mineral that shows fracturing (i.e. breaking irregularly). 5. Habit: the naturally occurring shape of a mineral (ex. Cubic, blocky, platy, etc). 2.2 INDIVIDUAL MINERAL PROPERTIES A. TECTOSILICATES 3D framework, comprise 75% of the Earth s crust 5

6 QUARTZ Formula: SiO 2 Color: Colorless to milky whitegrey H= 7 Streak= White Concoidal fracture (breaks like glass) Habit: Crystalline(left) or amorphous(right) B. FELDSPAR FAMILY ORTHOCLASE Formula: KAlSi 3 O 8 Color: Reddish-pink H= 6 Streak=White One perfect, one good cleavage Habit: Blocky, equant crystals Micro (perthitic) veining is common ALBITE Formula: NaAlSi 3 O 8 Color: Transparent to milky white H=6-7 Streak=White One perfect, one good cleavage Often confused with Quartz, but distinguished by uneven and blocky surfaces C. PHYLLOSILICATES BIOTITE Formula: K(Mg,Fe) 3 (AlSi 3 )O 10 (OH) 2 Color: dark brown to blackish brown H=2.5-3 (scratched by fingernail or coin) Streak=grey One perfect cleavage Habit: lamellar with platy, flexible plates Hexagonal outline of crystals 6

7 MUSCOVITE Formula: KAl 2 (AlSi 3 )O 10 (OH) 2 Color: typically colorless, but thickness adds tint of brown, yellow or pink H=2.5-3 (scratched by fingernail or coin) Streak= white Luster: pearly, vitreous; transparent/translucent sheets Perfect cleavage Not resistant to chemical weathering and often transformed to clay Common in Schists and Gneisses SERICITE Formula: Color: light brown H=2.5-3 (scratched by fingernail or coin) Streak=white Luster: transparent/translucent sheets, but higher luster and greasiness compared to Muscovite Common hydrothermal alteration mineral of Orthoclase and Plagioclase Feldspar TALC / SOAPSTONE Formula: Mg 3 Si 4 O 10 (OH) 2 Color: grey-white, yellow-white H=1 (scratched by fingernail) Luster: pearly Uneven fracture pattern Habit: can have minor foliation or uniformly indistinguishable crystals in masses Formation: Caused by the weathering of Magnesium (Mg) due to heat and water ILLITE Formula: (K,H 3 O)(Al,Mg,Fe) 2 (Si,Al) 4 O 10 [(OH) 2 H 2 O Color: white H=1-2 (between Talc and Gypsum) Habit: commonly found in aggregates A K-deficient Muscovite, non-expanding and found in masses 7

8 CHLORITE Formula: (Mg,Fe) 3 (Si,Al) 4 O 10 (OH) 2 (Mg,Fe) 3 (OH) 6 Color: Black with a tint of green H=2-2.5 (scratched by fingernail) Streak= pale green to grey Luster: vitreous Perfect cleavage with lamellar fracturing Habit= Usually found in aggregates/clusters of flakes Classified between a mica and clay D. INOSILICATES/AMPHIBOLE GROUP HORNBLENDE Formula: (Ca.Na) 2-3 (Mg,Fe,Al) 5 Si 6 (Al,Si) 2 O 22 (OH) 2 Color: Black to dark green H=5-6 (scratched by steel blade) Streak= pale grey Luster: lustrous to dull Imperfect cleavage and uneven fracture E. CARBONATES CALCITE Formula: CaCO 3 Color: white H=3 (scratched by coin) Habit= rhombohedra; crystals present in clusters of grains or small flakes Reacts to HCl EVAPORITES GYPSUM / ROCK GYPSUM as sedimentary rock Formula: Color: white-grey H=2 (scratched by fingernail) Texture: greasy and fibrous Luster: Translucent One perfect cleavage, but typically massive Note: For Limestone and Dolostone properties, see rock section 8

9 2.3 ROCKS Similar to minerals, rocks also have distinguishing features. Grain size is the most important characteristic used for rock identification. In the case of igneous rocks, they are classified as extrusive (volcanic) vs. intrusive (plutonic) rocks, which are differentiated by the size of crystals present in the matrix (the finer-grained material that larger grains/crystals are embedded within). For sedimentary rocks, they are classified as clastic/fragmental vs. crystalline rocks, but grain size is only the feature used to differentiate between the former category and the reaction to hydrochloric acid (HCl) determines the latter category. A second important characteristic is the degree of deformation of a rock and it is used for metamorphic rocks. There are low-, medium- and high-grade metamorphic rocks which have an increasing degree of deformation, however, this isn t a one-rule fits all and the mineral assemblage is the ultimate judge for metamorphic rocks (as some minerals are restricted by temperature (T) and pressure (P) conditions)) INDIVIDUAL ROCK PROPERTIES A. IGNEOUS ROCKS BASALT CLASS: Extrusive (Volcanic) Color: Black Grain size: aphanitic (grains not visible to naked eye) to fine-grained May contain few crystals Can contain vesicles due to the release of gas (picture on right) Formation: Low silica lava, formed at divergent plate boundaries (ex. Mid-oceanic ridges) GRANITE CLASS: Intrusive (Plutonic) Color: grey crystals (Quartz), white (Plagioclase), beige (Alkali Feldspar), black (Biotite, Hornblende) Grain size: typically coarse-grained (>1cm), with well-define crystals Composition: Qtz-Plag-Felds-Bio-Horn Formation: Silica-rich magma, intruding through the Earth s crust and cooling slowly 9

10 B. SEDIMENTARY ROCKS CONGLOMERATE /BRECCIA CLASS: Clastic/fragmental Color: variable Grain size: pebble clasts (rounded or angular) in sand, silt and/or clay matrix Formation: accumulation and deposition of varying sized particles/grains (i.e. cementation) SANDSTONE CLASS: Clastic/fragmental Color: variable Grain size: mm Pinro Occurs with faint or prominent layering Formation: accumulation of sand-sized particles, and slow deposition of grains into layer MUDSTONE/CLAYSTONE/SILTSTONE CLASS: Clastic/fragmental Color: variable Grain size: silt= mm, mud/clay=<0.004mm (grains not seen by the naked eye) H= ~1-2 (scratched by fingernail) Formation*: Conglomerate/breccias, sandstones and mudstone/claystone/siltstone form from sedimentation in a water body (eroded particles carried in suspension in the water, then are slowly deposited and compacted by overlying pressure) 10

11 SHALE CLASS: Clastic/fragmental Color: Dark grey Grain size: composed of clay particles (grains not seen by the naked eye) A mudstone that is fissile (i.e. breaks along bedding planes) LIMESTONE CLASS: Organic Color: White Reacts to HCl (only if powdered) Weathering from water forms carbonic acid. Common to have uneven surfaces leading to Karst environment (seen in picture on left) Areagaad Formation: composed of seafloor bed remains (micro shells), compressed under pressure Bholna DOLOMITE/DOLOSTONE CLASS: Crystalline Color: light pink, but dark grey weathered surface Weathered surface shows Elephant skin texture H=3.5-4 Habit=crystalline form has small saddle-shaped crystals Little reaction to HCl Formation: low temperature, high salinity/sedimentary basins environments 11

12 C. METAMORPHIC ROCKS SLATE CLASS: Low-grade Color: Dark grey to black Grain size: Aphanitic to fine-grained Composition: clay with Qtz-Mus-Ill-Bio-Chl Foliated, homogeneous H= softer than glass Parent rock = Shale Formation: regional metamorphism (low T and P) Nawli PHYLLITE CLASS: Low-grade Color: grey-green, but reddish-brown weathered surface Grain size: fine-grained Composition: Qtz-Ser- Chl +/- Felds, Amp, Gar High fissility Formation: regional metamorphism (greater T and P compared to Slate, but less than Schist) (MICA) SCHIST CLASS: Medium-grade Grain size: fine Composition: >50% platy & elongated minerals with Qtz-Felds-Micas-Chl-Talc- Horn +/- Graphite, Garnet Schistocity (from lamellar mineral) Classified according to dominant mineral Chopra Formation: regional metamorphism (greater T and P compared to Phyllite, but less than Gneiss) 12

13 GREEN SCHIST CLASS: Medium-grade Grain size: fine Color: green to greyish-brown Dominant mineral: Chlorite, whereas remaining composition: >50% platy & elongated minerals with Qtz-Felds-Micas-Talc-Horn Common schistocity (sheen from lamellar minerals) Formation: regional metamorphism (greater T and P compared to Phyllite, but less than Gneiss) TALC SCHIST CLASS: Mediumgrade Grain size: very fine Color: white-grey Dominant mineral: Talc Fibrous and greasy texture Areagaad Formation: regional metamorphism (greater T and P compared to Phyllite, but less than Gneiss) Doba Formation: regional metamorphism (greater T and P compared to Schist) GNEISS CLASS: High-grade Grain size: coarsegrained Color: white (Plagioclase) and black (Amphibole) segregation of minerals Typically foliated/parallel layers Parent rock= Granite 13

14 AUGEN GNEISS CLASS: High-grade Augen = eye-shaped Grain size: coarse-grained Color: white and black segregation of minerals Eye-like crystals are pinched and ends are stretched Layers are folded Parent rock= Granite Formation: regional metamorphism (greater T and P compared to Schist) Pinro QUARTZITE CLASS: High-grade Grain size: medium to coarse-grained Color: beige to pink, but red due to iron oxide. Weathered surface can be dark grey Typically non-foliated Parent rock= Sandstone Formation: Related to regional metamorphism Pinro high compression Quartz grains re-crystallize and cement together to form interlocking mosaic of grains MARBLE CLASS: High-grade Grain size: fine to medium-grained Color: white to beige Well-defined crystals have high luster Typically non-foliated Parent rock= Limestone or Dolostone Formation: regional or contact metamorphism; recrystallized minerals (Calcite or Dolomite) 14

15 SECTION 3: METAMORPHISM & ALTERATION 3.1 METAMORPHISM There are 3 main types of metamorphism: Regional: a large area of continental crust is involved in mountain range formation (convergent plate boundaries) leading to extreme compression conditions Contact: occurring around intrusive igneous rocks (ex. Granite). High temperature gradient is produced locally around intruding magma. Hydrothermal: High temperature environment where fluid (usually water or air) interacts with pre-existing rock. Metasomatism occurs (i.e. chemical alteration of the rock leading to the formation of new mineral assemblages). 3.2 ALTERATION The two main types of alteration discussed in this section are physical and chemical alteration. Physical alteration in rocks refers to a change in appearance, from folding (referred to as plastic deformation) or faulting (referred to as brittle deformation). Deformation is in reference to the degree of strain required to break the rock. Chemical alteration in rocks describes a change in the mineral assemblage (i.e. different minerals are only stable at certain pressure and temperature conditions). An explanation of the latter type of alteration can be assisted by Figure 3. Figure 3. Amphibolite to Greenschist reaction The majority of rocks are subject to alteration, but in simpler terms, this often means that one mineral is replaced by another due to a chemical reaction. Figure 3 shows that the mineral assemblage present in the Amphibolite facies: Garnet (gt) + Hornblende (hbl) + Plagioclase (plag) Changes to the Greenschist facies with the mineral assemblage: Chlorite (chl) + Actinolite (act) + Epidote (ep) is stable Due to decreasing temperature, but constant pressure (as previously seen in Figure 2). Another type of chemical alteration is silification and it occurs when the rock s environment is changed by the introduction of a Silica-rich fluid. This coats the pre-existing rock with this fluid and thus, alters the hardness of the rock to be equivalent to that of Quartz (H=7). 15

16 In summary, the geology across the area where CHIRAG is presently working is very diverse ranging from sedimentary environments to low- and high-grade metamorphism (see Table 4). Table 4. Local geology around CHIRAG areas Region Main Geology Spring type Reetha Phyllite, Quartzite, Schist Fracture Kasiyalekh Phyllite, Quartzite, Gneiss Fracture Sualbaari Phyllite, Quartzite, Schist Contact, Fracture Kathpuria Limestone (Talc), Dolomite Karst Dewaldhar Limestone, Dolomite, Phyllite Karst Pinro Quartzite, Green Schist, Phyllite Fracture The different rock types in each area controls the type of the spring (called the structural control). For example, fracture springs occur in rocks with a high tendency to break (i.e. brittle deformation) and this leads to the formation of joints which are parallel or perpendicular passages for water to pass through. Contact springs occur where overlying rocks have varying integrities (i.e. one rock has hig her permeability or higher brittle deformation so water favors that pathway compare the other adjacent rock). In the case of karst springs, the reaction of limestone with water forms carbonic acid, which carves pathways in the rock where water easily flows. Moreover, specific rock properties such as how sorted the grains are or the nature of fractures play an extremely important role in terms of increasing the rock s storativity of water. For example, a well-sorted Sandstone (see Figure 4) has a higher storage capacity of water compared to an unsorted Sandstone. On the other hand, a fractured Shale has a higher storage capacity as the individual cracks form a large network where water can flow (an unfractured rock has pockets of water which cannot be connected). Figure 4. Sortedness of a Sandstone and Figure 5. Fractures in a Shale 16

17 APPENDIX Suggestions for geologic field tools: 1. Hand lens (18x magnification, 18-21mm viewing field) Purpose: magnified view of microscopic minerals and features present in field specimen Unit Price: ~ $5.00 USD 2. Dual magnetic pen & engineering tungsten scriber Purpose: to determine magnetic properties and specific hardness of minerals & rocks Unit Price: ~$8.00 USD (10% discount 10+ purchased, 40% discount 20+ purchased) 3. Metric protractor Purpose: to measure angle and length of linear features (bedding, foliation) in rocks Unit Price: ~$4.00 USD 4. Acid bottle (empty) Purpose: to determine presence of carbonaceous minerals (fill with hydrochloric acid) Unit Price: ~$1.00 USD 5. Field sample cards (grain size card or rock texture cards) Purpose: pocket-sized cards with useful properties to compare to field specimens Unit Price: ~$ USD 17

18 6. Streak Plates (white or black) Purpose: to test the color of a mineral s streak which is one method aiding in its identification Unit Price: only come in packs of 10 for ~$5.00 USD REFERENCES: (rock properties) Figure 1: Figure 2 & 3: Figure 4 & 5: Dr. Jeffrey Mckenzie s slideshow, McGill University lecture (2011) 2.2 MINERALS Quartz (Crystallie Quartz) (Amorphous Quartz) Orthoclase O.htm Albite Biotite Muscovite Sericite Chlorite Talc Illite Hornblende Calcite Gypsym ROCKS 18

19 Basalt (Vesicular Basalt) Granite Conglomerate Breccia Sandstone (layered) Shale Mudstone/Claystone/Siltstone Dolomite Limestone Slate Phyllite Mica Schist Green Schist Talc Schist Gneiss Augen Gneiss Quartzite Marble *Remainder of photographs in this manual were taken by Sophia Yee 19