浅成低温热液矿床

Characteristics and Genesis of Epithermal Gold Deposits 浅成低温热液金矿 特点及成因 Low Sulfidation 第二部分：低硫化浅成低 温矿床 David Cooke, J Bruce Gemmell and Noel White Crustiform banded low sulfidation vein, McLaughlin gold deposit, California Vuggy quartz, Yanacocha district, Peru LS Deposit Characteristics LS矿床特征 Ore矿石 Au-Ag Metals 金属 As, Sb, Zn, Pb, Hg, Se Alteration adularia-carbonate, illite (muscovite), smectite, chlorite, epidote 蚀变 冰长石-碳酸盐，伊利石 （白云母），蒙脱石，绿泥 石，绿帘石 Textures Open space fill（banded crustiform veins, bladed calcite,breccias) 结构 开放空间充填（壳状条纹 脉，叶片状方解石，角砾岩 Form Veins, breccias, disseminations 形态 脉状，角砾状 ，浸染状 Serujan deposit, Mt Muro, Indonesia Low Sulfidation (LS) Deposits 低硫化矿床 2 k m 2 km • Magmatic heat source (plus volatiles?) 岩浆是热源（也 是挥发份源？） Magma 岩浆 Magma 岩浆 acid sulfate steam-heated waters mud pools, fumaroles • Steam-heated acid sulfate waters 蒸汽加热的酸性硫 酸盐水 CO2-rich steam- heated waters • Peripheral bicarbonate waters 外围的重碳酸盐水 • Meteoric convection 大气水对流 chloride waters boiling springs, silica sinter 400ºC Neutral chlorideNeutral chloride LS watersLS waters cold groundwater recharge 冷地下水补充 中性氯化物 低硫化水 富CO2的蒸汽加热的水 蒸汽加热的酸性硫酸盐 水，泥池，喷气孔 氯化物水，沸腾泉， 硅酸盐泉华 Pajingo - Jandam 685HWPajingo - Jandam 685HW Low Sulfidation Deposits 低硫化矿床 Low Sulfidation Deposits 低硫化矿床 脉状矿体，有条纹 Banded vein ore, Hishikari, Japan 脉状矿体，有条纹 Banded vein ore, Hishikari, Japan 网脉状矿体 Stockwork ore, Guanajuato, Mexico 网脉状矿体 Stockwork ore, Guanajuato, Mexico 角砾岩中赋存的矿体 Breccia-hosted ore, Kelian, Indonesia 角砾岩中赋存的矿体 Breccia-hosted ore, Kelian, Indonesia Low Sulfidation Deposits 低硫化矿床 Low Sulfidation Deposits 低硫化矿床 Silver sulfosalts, Mt Muro, Indonesia 银的硫盐矿物 Silver sulfosalts, Mt Muro, Indonesia 银的硫盐矿物 Free gold,Porgera, PNG (Corbett & Leach, 1998) 自然金 ， Free gold,Porgera, PNG (Corbett & Leach, 1998) 自然金 ， Metallic minerals include: electrum, acanthite, Ag-sulfosalts, sphalerite, galena, tetrahedrite- tennantite, chalcopyrite, arsenopyrite, pyrrhotite, selenides, tellurides 金属矿物包括：银金矿，螺状银硫矿，银的硫盐矿物，闪锌矿，方铅矿，黝铜矿-砷黝铜 矿，黄铜矿，毒砂，磁黄铁矿，硒化物，碲化物。 LS ore mineralogy LS 矿物矿石 • SiO2 polymorphs (quartz, chalcedony, amethyst) SiO2的同质异形体(石英，玉髓，紫水晶) • Adularia 冰长石 • illite (sericite) 伊利石（绢云母） • Chlorite 绿泥石 • Carbonates (calcite, rhodochrosite) 碳酸盐（方解石，菱锰矿） • barite and fluorite 重晶石&萤石 Bimurra, Australia LS gangue mineralogy LS 脉石矿物 quartz, chalcedony, adularia 石英，玉髓，冰长石 quartz, chalcedony, adularia 石英，玉髓，冰长石 quartz, chalcedony, amethyst 石英， 玉髓， 紫水晶 quartz, chalcedony, amethyst 石英， 玉髓， 紫水晶 quartz, chalcedony 石英， 玉髓 quartz, chalcedony 石英， 玉髓 Quartz 石英 Quartz 石英 Golden Cross, New ZealandGolden Cross, New Zealand Guanajuato, MexicoGuanajuato, Mexico McLaughlin, California McLaughlin, California Victoria, PhilippinesVictoria, Philippines KAO PYR ADU 1 cm Gosowong, Indonesia Adularia-pyrite cemented breccia with late kaolinite overprint 冰长石-黄铁矿胶结角砾, 有高岭土叠加 Adularia-pyrite cemented breccia with late kaolinite overprint 冰长石-黄铁矿胶结角砾, 有高岭土叠加 Kelian, IndonesiaKelian, Indonesia Gosowong, IndonesiaGosowong, Indonesia quartz, adularia 石英 ， 冰长石 quartz, adularia 石英 ， 冰长石 Adularia rhombs intergrown with rhodochrosite and quartz 菱形的冰长石与菱锰矿和石英共生 Adularia rhombs intergrown with rhodochrosite and quartz 菱形的冰长石与菱锰矿和石英共生 Acupan, PhilippinesAcupan, Philippines Cracow, AustraliaCracow, Australia quartz, adularia 石英，冰长石 quartz, adularia 石英，冰长石 Clast of grey quartz vein overgrown by colloform calcite Clast of grey quartz vein overgrown by colloform calcite Acupan, PhilippinesAcupan, Philippines Kelian, IndonesiaKelian, IndonesiaKelian, Indonesia Kelian, Indonesia Bladed calcite overgrown by sphalerite 闪锌矿生长在叶片状的方解石上 Bladed calcite overgrown by sphalerite 闪锌矿生长在叶片状的方解石上 Rhodochrosite-cemented breccia 菱锰矿胶结角砾岩 Rhodochrosite-cemented breccia 菱锰矿胶结角砾岩 Cerro Vanguardia, ArgentinaCerro Vanguardia, Argentina quartz after bladed carbonate (lattice texture) 石英交代叶片状的碳酸盐（格子结构） quartz after bladed carbonate (lattice texture) 石英交代叶片状的碳酸盐（格子结构） Hedenquist et al, 1996 酸性的 中性的 碱性的 Examples of LS deposits LS矿床的例子 0 2 41 3 5 Lihir, Papua New Guinea: 147 Mt @ 2.7 g/t Au 41 Moz Au 0 2 41 3 5N Gosowong, Halmahera, Indonesia: 0.99 Mt @ 27 g/t Au, 38 g/t Ag 0.9 Moz Au N 0 2 41 3 5 0 2 41 3 5 N Cerro Vanguardia, Argentina: 15.9 Mt @ 8.3 g/t Au, 102 g/t Ag 4.3 Moz Au Mt Muro, Kalimantan, Indonesia: 8.3 Mt @ 3.2 g/t Au, 76 g/t Ag 0.9 Moz Au 10x Bimurra, Drumond Basin, Qld: 1.6 Mt @ 1.4 g/t Au 0.07 Moz Au 200 m 4x 1 km Post-mineral cover sequences Younger than host-rocks Host-rocks and approx. age equivalents Older than host-rocks Epithermal Au-Ag deposits Epithermal veins (low-grade – barren) Post-mineral faults Pre-to syn-mineral faults Bedding trend, dip indicated Syncline AnticlineScott, 2002 Moonlight prospect, Pajingo Champagne pool, NZ Ohaki, NZ 脉石矿物的垂直分带 Gangue Zonation – from surface to depth 表生沉积泉华（硅华），热液爆破角砾 Surface deposits – sinter, hydrothermal eruption breccias 脉石矿物的垂直分带 Gangue Zonation – from surface to depth 表生沉积泉华（硅华），热液爆破角砾 Surface deposits – sinter, hydrothermal eruption breccias Hammond (2004) Moonlight prospect, Pajingo Fresnillo, Mexico Moonlight prospect, Pajingo Hammond (2004) 脉石矿物的垂直分带 Gangue Zonation – from surface to depth 浅部：细粒石英-石髓脉，细脉体 Shallow: fine grained quartz- chalcedony veins, thin vein stockworks 脉石矿物的垂直分带 Gangue Zonation – from surface to depth 浅部：细粒石英-石髓脉，细脉体 Shallow: fine grained quartz- chalcedony veins, thin vein stockworks Hammond (2004) Cerro Vanguardia, ArgentinaCerro Vanguardia, Argentina Waihi, New ZealandWaihi, New Zealand Golden Cross, New Zealand Golden Cross, New Zealand Hammond (2004) 脉石矿物的垂直分带 Gangue Zonation – from surface to depth 梳状-层状石英-冰长石-硫化物脉 Crustiform banded quartz- adularia-sulfide veins 脉石矿物的垂直分带 Gangue Zonation – from surface to depth 梳状-层状石英-冰长石-硫化物脉 Crustiform banded quartz- adularia-sulfide veins Victoria, Philippines Below Nancy deposit, Pajingo Hammond (2004) 脉石矿物的垂直分带 Gangue Zonation – from surface to depth 粗粒自型梳层状石英 Coarse euhedral crustiform banded quartz 脉石矿物的垂直分带 Gangue Zonation – from surface to depth 粗粒自型梳层状石英 Coarse euhedral crustiform banded quartz Corbett and Leach, 1998 Metal Zonation 金属分带 Zn Sb As Ag Au Cu Hg Pb 矿物分带 Mineralogical Zoning LOW SULFIDATION 低硫化作用 Crustiform banded ore with lattice textures 有格子结构 的壳状的条带矿石 Altered host rock 蚀变围岩 smectite蒙脱石 illite伊利石 pyrite黄铁矿 illite伊利石 chlorite 绿泥石 calcite方解石 pyrite黄铁矿 epidote绿帘石 quartz石英 adularia冰长石 illite伊利石 pyrite黄铁矿 quartz, chalcedony, adularia, pyrite, base metal sulfides, carbonates, Au-Ag 石英，玉髓，冰长石， 黄铁矿，贱金属硫化物 ，碳酸盐， Au-Ag Modified from Sillitoe, 1993 HIGH SULFIDATION 高硫化作用 Disseminated or massive ore 浸染状或块状矿石 smectite 蒙脱石 illite / chlorite 伊利石/ 绿泥石 chlorite 绿泥石 calcite 方解石 epidote 绿帘石 quartz, alunite 石英， 明矾石 residual quartz (vuggy & massive), alunite, sulfides, sulfosalts, Au-Cu-(Ag) 残余石英（多孔状& 块状），明矾石，硫 化物，硫盐，金铜银 Kaolinite (pyrophyllite?) ± sericite / illite Altered host rock 蚀变围岩 1 - 10 m Hedenquist et al. (2000), modified from Buchanan (1981), Sillitoe (1993) 高岭土 ± 明矾石 ±自然硫-蛋白石（蒸汽热蚀变） 热泉 泉华层地下水位 石髓层 可透岩层 侵染状矿石 脉状矿石 绢云母/伊利石 ±冰长石 绿泥石-方解石 ±绿帘石 蒙脱石/混层粘土 ±绿泥石 梳状石英/石髓-碳酸盐 ±冰长石 ±重晶石/萤石 • Decompressional boiling can cause: 减压沸腾可以引起：  loss of gases (H2O, CO2, H2S) 气体的损失（主要是H2O, CO2, H2S）  increase in pH pH值的增加  increase in oxidation state 氧化态的升高 Salinity increase (slight) 盐分的增加（轻微的） deposition of gold, adularia, bladed calcite 金，冰长石，叶片状方解石的沉 积 Boiling of Hydrothermal Fluids 热液流体的沸腾 Crested Pool, Upper Geyser Basin, Yellowstone, USA. Adularia - Kelian, Indonesia 冰长石 Adularia - Kelian, Indonesia 冰长石 Bladed calcite - Golden Cross, New Zealand 叶片状的方解石 Bladed calcite - Golden Cross, New Zealand 叶片状的方解石 Evidence of Boiling 沸腾的证据 Evidence of Boiling 沸腾的证据 Co-existing L- and V-rich fluid inclusions, Acupan, Philippines 共存的富液相和富气相流体包裹体 Co-existing L- and V-rich fluid inclusions, Acupan, Philippines 共存的富液相和富气相流体包裹体 Hydrothermal eruption breccia, Yellowstone, USA 热液喷发角砾岩 Hydrothermal eruption breccia, Yellowstone, USA 热液喷发角砾岩 Romberger, 1993 Boiling and Au Deposition 沸腾和金沉淀 Au(HS)2- + H+ + 0.5 H2 (g) Auo + 2H2S • Steam and other gases accumulate beneath a silica seal during upflow of boiling waters 当沸腾的液体上升时水蒸汽和其他气体汇聚在硅质密封层之下 • Gas pressure build-up can rupture the hydrothermal seal, triggering a steam explosion & phreatic brecciation 内部的气体压力集聚，可以撕裂热液密封层，引起蒸汽爆发&角砾化 Gas cap in self-sealed geothermal system (Hedenquist & Henley, 1985) Phreatic Breccias 热液角砾岩 D e p t h ( m ) 深 度 20 40 200 400 Pressure (bars) Hot Spring 温泉 Eruption Vent 喷出口 Boiling water 沸腾水 Water 水 Silica seal Gas Cap Multi-stage vein breccia, Palmerejo, Mexico • Depressurisation affects a significant vertical column of rock (100s of metres) and can trigger ore deposition 减压作用影响几百米深的岩石，可以引发矿石沉淀 E x t e n t o f B r e c c i a t i o n Ore Deposition 矿石沉淀 Low sulfidation 低硫化作用 • Boiling is the principal mechanism 沸腾是主要的机制 • Mixing may occur during collapse of the hydrothermal system 混合作用可能发生在热液活动减弱过程中 High sulfidation 高硫化作用 • Unequivocal evidence for fluid mixing at some deposits 在某些矿床中有流体混合确切的证据 • Boiling is a viable mechanism for deposits where gold is transported as a bisulfide complex 沸腾在金以硫氢根络合物形式运移时是可 行的沉淀机制 Electrum, tellurides & base metal sulfides, Acupan, Philippines 但不要指望会发现金疙瘩 But don’t expect to find nuggets! • 岛弧或者弧后火山岩带 Arc or back-arc volcanic belt  陆相 subaerial • 寻找脉体，蚀变及泉华（硅华）的证据 veins, alt., sinter• 区域磁异常能有帮助 Regional magnetics can help  去磁性 demagnetisation • 寻找蚀变 Look for alteration  记住分带 remember zoning • 地球化学 Geochemistry  金，银，砷，锑，锌，铅，铜 Au, Ag, As, Sb, Hg, Zn, Pb, Cu • 寻找矿化 Look for mineralisation  记住结构，浮动 remember textures, float! • 浅层剥蚀 Not deeply eroded  有利于沉降 subsidence favourable • 对蒸汽热蚀变带要注意 Beware of steam-heated zones! • 做好持久钻探的准备 Be prepared to drill, drill and drill… 勘探 Exploration