GEORGETOWN QUARTZ TEXTURES

Transcription

1 GEORGETOWN QUARTZ TEXTURES NOV 2017 Ashley Cody, Harry Mustard, Gregg Morrison

2 GEORGETOWN METALLOGENIC STUDY INTRODUCTION AND OBJECTIVES FUNDED BY GEOLOGICAL SURVEY OF QUEENSLAND REVITALISE EXPLORATION IN GEORGETOWN REGION THROUGH UPDATED METALLOGENIC DATABASE AND MODEL FOR REGION STUDY UPDATED WITH RECENT EXPLORATION DATA, AGE DATING, MULTI-ELEMENT GEOCHEMISTRY AND IMPROVED UNDERSTANDING OF MINERAL DEPOSITS IN NORTH QUEENSLAND

3 WORK COMPLETED IN THE 2017 QUARTZ TEXTURES STUDY 1. COLLECTION SAMPLES OF QUARTZ ASSOCIATED WITH MINZ TO STUDY TEXTURES, STYLE OF MINZ AND CONDITIONS UNDER WHICH QUARTZ FORMED 2. MINES AND MINERAL OCCURRENCES WITH A COMMON ORIGIN GROUPED INTO CAMPS 3. REPORT PREPARED INCLUDING A DATABASE AND METALLOGENIC MAPS FOR THE REGION

4 GEORGETOWN QUARTZ TEXTURES 133 historical mines inspected and sampled Most mineral deposits in Georgetown region possess quartz as a gangue to mineralisation Morphology and texture of quartz are a good indicator of conditions under which quartz and associated mineralisation was formed Quartz textures indicative of origin Mines and mineral occurrences with a common origin grouped into Camps

5 1. Buck CLASS QUARTZ CLASSIFICATION SCHEME GRAIN SIZE INTERNAL VARIABILITY GRAIN FORM CRYSTAL PACKING (a) Anhedral Variable High Anhedral Tight None PREFERRED GRAIN ORIENTATION (relative to substrate) (b) Euhedral Variable High Prismatic Tight Random 2. Fibre Variable Low Fibrous Tight Orthogonal 3. Comb (a) Coarse Coarse Low Prismatic Moderate Prismatic (b) Medium Medium Low Prismatic Moderate Prismatic (c) Fine Fine Low Prismatic Open Prismatic 4. Banded (a) Crustiform Variable Low Variable Tight Orthogonal (b) Colloform Variable Low Variable Tight Orthogonal (e) Cockade Variable Low Radial Tight Orthogonal 5. Saccharoidal Variable Low Anhedral Moderate None 6. Laminated Variable Low Anhedral Tight Parallel 7. Ribbon ¹ 8. Stylolite¹ 9. Spider (a) Comb Fine Low Prismatic Moderate Orthogonal (b) Phantom Fine Low Mimics Host Tight Mimics Host 10. Breccia (a) Infill Variable High Prismatic Variable Variable (b) Aggregate Variable High Anhedral Variable Variable 11. Replacement Variable Low Mimics Host Mimics Host Mimics Host (From Dowling and Morrison, 1990)

6 1. Buck: TEXTURAL TYPE MINERAL SYSTEM BASED ON QUARTZ TEXTURES EPITHERMAL INTRUSION RELATED PLUTONIC (a) Anhedral (b) Euhedral Fibre Comb: (a) Coarse (b) Medium 4. Banded: (c) Fine (a) Crustiform (b) Colloform (e) Cockade 5. Saccharoidal Laminated Ribbon ¹ Stylolite¹ Spider: (a) Comb (b) Phantom Breccia: (a) Infill (b) Aggregate Replacement Sample suites describe: primary quartz textures assemblage Deformation textures Order of formation and relative abundance Ore location Interpret three mineral systems at Georgetown: Plutonic Intrusion Related Epithermal And relative depth of formation: Hypozonal Mesozonal Epizonal From Dowling and Morrison 1990

7 COMMON QUARTZ STYLES FOUND IN ETHERIDGE PROVINCE BRECCIATED EUHEDRAL BUCK PLUTONIC HYPOZONAL COARSE COMB QUARTZ PLUTONIC HYPOZONAL INTRUSION RELATED MESOZONAL INTRUSION RELATED EPIZONAL FINE COMB SACCHAROIDAL AND SILICA-SULFIDE

8 QUARTZ TEXTURES OF PLUTONIC DEPOSITS Gold Bearing quartz Quartz textures indicative of the Plutonic mineralising environment were most common; 101 of the 133 deposits visited. Sheared Host rock lode Often hosted in steep dipping shears or lodes cutting Proterozoic granite and metamorphic rocks. Lodes can be of significant size; i.e. km s length and 10 s metres width; however individual quartz veins tend to be irregular or lenticular in shape and rarely exceed 50 cm thickness and 20 m length. This is due to irregular development of tensional zones during fault movement, brittleness of host rocks and deformation by later fault movement.

9 QUARTZ TEXTURE ASSEMBLAGES AND CAMP DEFINITION CODES DEFINED FOR EACH QUARTZ TEXTURE AND DEFORMATION FEATURE INDIVIDUAL DEPOSITS ASSIGNED CODES BASED ON ORDER OF ABUNDANCE MINERAL DEPOSITS WITH SIMILAR CODES OCCURRING IN SAME AREA GROUPED INTO CAMPS 51 CAMPS DEFINED IN GEORGETOWN FORSAYTH GILBERTON REGION 32 PLUTONIC, 15 INTRUSION RELATED AND 4 EPITHERMAL CAMPS IN REGION

10 QUARTZ TEXTURES OF PLUTONIC DEPOSITS EARLY COARSE EUHEDRAL BUCK QUARTZ FOUND IN MANY DEPOSITS IS NEARLY ALWAYS RECRYSTALLISED BY LATER SHEARING BRECCIATION PRODUCING EQUIGRANULAR TEXTURE OF ANHEDRAL GRAINS OBLITERATING OR MASKING ORIGINAL QUARTZ TEXTURES DEFORMATION OF EARLY QUARTZ LEADS TO BRECCIA AND VEINS INFILLED BY FINER COMB QUARTZ AND DEVELOPMENT OF SPIDER VEINLETS AND STYLOLITES LATER PHASES O QUARTZ OFTEN ACCOMPANIED BY SULPHIDES THAT ARE USUALLY RESPONSIBLE FOR GOLD AND BASE METAL MINERALISATION MULTIPLE CROSSCUTTING QUARTZ EVENTS WITH DIFFERENT TEXTURES LATER QUARTZ PHASES TEND TO BE FINER GRAINED; INDICATIVE OF SHALLOWER DEPTH OF FORMATION THAN EARLIER PHASES BRECCIA WITHIN LODES DOMINATED BY BRITTLE TEXTURES AND RARELY ANY DUCTILE FABRIC

11 QUARTZ TEXTURES OF PLUTONIC DEPOSITS JOSEPHINE GOLDMINE Plutonic Hypozonal Early coarse buck quartz fractured, deformed and recrystallised by shearing 9.59 g/t Au, 183 g/t Ag JOSEPHINE GOLDMINE Plutonic Hypozonal Deformation of early quartz produces breccias and veins often filled with finer grained quartz and sulphides that introduce the gold

12 QUARTZ TEXTURES OF PLUTONIC DEPOSITS 336 g/t Au 498 g/t Ag MOUNT HOGAN Plutonic Mesozonal Early medium grained euhedral buck quartz fractured, brecciated and recrystallised with open space filled by pyrite, chalcopyrite and galena. CENTRAL GEORGETOWN AND FORSAYTH DISTRICTS Plutonic Mesozonal 24.9 g/t Au g/t Ag Early medium, white euhedral buck quartz fractured and cut by fine, clear quartz spider veinlets and minor stylolites. Disseminated sulphide minz introduced along late fractures.

13 QUARTZ TEXTURES OF INTRUSION RELATED DEPOSITS INTRUSION RELATED QUARTZ GENERALLY FINER GRAINED THAN PLUTONIC CATEGORY TEXTURES COMMONLY FINE TO MEDIUM COMB QUARTZ IN VEINS, STOCKWORK OR BRECCIA EARLY PHASES OFTEN CUT BY LATER FINE COMB QUARTZ LIKE PLUTONIC DEPOSITS, INTRUSION RELATED DEPOSITS ALSO SUBDIVIDED INTO MESOZONAL AND EPIZONAL BASED ON NATURE OF MINERALISATION AND FINENESS OF QUARTZ TEXTURES DEPOSITS ARE OFTEN HOSTED IN PERMO-CARBONIFEROUS AGE INTRUSIVES OR SPATIAL ASSOCIATION WITH THEM; e.g. MOUNT TURNER, ELECTRIC LIGHT, CUMBERLAND, KIDSTON, LOG CREEK, MOUNT MCDONALD, HUONFELS

14 QUARTZ TEXTURES OF INTRUSION RELATED DEPOSITS EASTERN BAR Intrusion Related Mesozonal 0.03 g/t Au 179 g/t Ag 70.9 g/t Au 50.6 g/t Ag Vuggy, medium comb quartz infill of brecciated granite and schist. Euhedral quartz crystals are zoned, not deformed and cores to vugs filled with limonite after sulphides. ELECTRIC LIGHT Intrusion Related Epizonal Rhyolite breccia ore. Early phase brecciation cemented by fine black silica-pyrite cut by stockwork of clear to white, fine comb quartz; saccharoidal.

15 QUARTZ TEXTURES OF EPITHERMAL DEPOSITS EPITHERMAL QUARTZ TEXTURES WERE LEAST COMMON IN GEORGETOWN FORSAYTH - GILBERTON REGIONS ONLY EIGHT OUT OF 133 SITES VISITED WERE EPITHERMAL COLLOFORM AND CRUSTIFORM BANDED CHALCEDONY AND VERY FINE COMB IN STOCKWORK OR AS BRECCIA INFILL ALL DEPOSITS HAD CLOSE ASSOCIATION WITH PERMIAN AGE VOLCANICS AND INTRUSIONS

16 QUARTZ TEXTURES OF EPITHERMAL DEPOSITS +100 g/t Au 42 g/t Ag AGATE CREEK, FORSAYTH Epithermal Polymict hydrothermal breccia composed mostly of rhyolite angular clasts cemented by cryptocrystalline quartz. Cut by later fine veinlets of clear quartz. PERCY QUEEN, PERCYVALE Epithermal 11.3 g/t Au 151 g/t Ag Hydrothermal brecciated rhyolite cemented by very fine comb quartz and fine silica-pyrite (darker patches).

17 PLUTONIC HYPOZONAL Early coarse euhedral buck quartz MINERAL DEPOSIT TYPE BY BY QUARTZ TEXTURES PLUTONIC MESOZONAL Coarse comb quartz (early coarse euhedral buck) INTRUSION RELATED MESOZONAL Med-fine comb quartz as veins +/- breccia infill +/- fine comb quartz INTRUSION RELATED EPIZONAL Med-fine comb quartz as veins +/- breccia infill EPITHERMAL Chalcedony, crustiform +/- colliform banding (fine comb quartz) Brecciated and recrystallised by shearing Stylolitic and spider veinlets +/-Au (As) Brecciated and recrystallised by shearing Fine comb veins (stylolitic and spider veinlets) Vuggy medium comb; zoned Early phase brecciation cemented by silica-pyrite and stockwork Saccharoidal; fine comb Crustiform-colloform banded chalcedony; very fine comb in stockwork or breccia infilling; replacement Gold and sulphides in late stage; fine comb quartz +/- base metals Fine comb quartz; gold and sulphides in late stage Vugs infilled with sulphides + Au Infill of breccia with fine black silica-pyrite EXAMPLES OF DEPOSITS, MINES AND CAMPS: Four Gees; Dairy Maid; Glenrowan; Goldsmiths; International; Gilberton Camp Big Reef; Big Wonder; Christmas Hill; Bald Carbon Copy; Mountain; Electric Light; Havelock; Durham; Dry Green Hills; Huonfels Hash; Drummer Hill; Cumberland Camp; Georgetown Camp Cumberland Mine; Beverley Mine Agate Creek (Sherwood); Woolgar; Percy Queen (Percyvale) Newcastle Range (Cornucopea; Collins Creek)

18 EXAMPLES OF MINERALISATION STYLE AND ENDOWMENT PLUTONIC HYPOZONAL PLUTONIC MESOZONAL INTRUSION MESOZONAL INTRUSION EPIZONAL EPITHERMAL International, Georgetown 1,150 kg Titania, Georgetown 535 kg Mount Hogan, Gilberton 2,700 kg Woolgar (Mes) 37,227 kg Kidston, Einasleigh 150,000 kg Christmas Hill Einasleigh 30 kg Cumberland, Georgetown 1,900 kg Electric Light, Georgetown 1,500 kg Agate Creek, Forsayth 15,985 kg Woolgar(Epi) 21,887 kg Beverley, Einasleigh Goldsmiths, Forsayth 420 kg Durham, Georgetown 2,200 kg 460 kg Queenslander, Forsayth 1,420 kg

19 CLASSIFICATION OF DEPOSITS BY QUARTZ TEXTURE MAP SHOWING DISTRIBUTION OF THREE MAIN DEPOSIT TYPES IDENTIFIED THROUGH THE GEORGETOWN, FORSAYTH AND GILBERTON AREAS: EPITHERMAL INTRUSION RELATED PLUTONIC

20 DISTRIBUTION OF MINE CAMPS BY QUARTZ TEXTURE Mining districts of Georgetown and Forsayth are dominated by Devonian Plutonic Hypozonal and Mesozonal style deposits, lesser Intrusion Related and few Epithermal. Zoning from deeper to shallower level away from centres of each plutonic districts. The Carboniferous Intrusion-Related and Permian Epithermal Camps are partly overprinting but mainly peripheral to the Plutonic camps and localised by volcanic to sub-volcanic complexes and regional lineaments Quartz texture assemblages are a useful tool for deposit classification, especially in conjunction with multi-element geochemistry