研究生知识库

黔西南地区是我国滇黔桂“金三角”的重要组成部分，区内发育水银洞、泥堡、烂泥沟和丫他等一大批大型超大型卡林型金矿床。本区从寒武纪至中三叠世为海相沉积，晚三叠世以来为陆相沉积，区内出露的泥盆系、石炭系、二叠系和三叠系地层均发育良好。其中，二叠系和三叠系的海相沉积岩地层是卡林型金矿床最主要的赋金地层。地质构造主要为在印支期和燕山期形成的造山型褶皱和断裂，以复式褶皱为主，近东西向展布。岩浆活动微弱，地表出露的火成岩较少。根据矿体形态、产状、控矿构造和赋矿层位等黔西南地区卡林型金矿床可分为层控型、断控型和层控—断控复合型等主要类型。层控型金矿床的矿体在空间上常呈分层产出，产状与地层产状基本一致，受控于地层的层间滑脱构造以及茅口组与龙潭组之间的区域性不整合面；断控型金矿床的矿体主要赋存于主断裂及其次级断裂破碎带中，产状受高角度压扭性断裂构造控制；复合型金矿床兼备层控型和断控型两种控矿构造，如水银洞、泥堡、簸箕田和紫木凼金矿床。选取水银洞和泥堡金矿床作为研究对象，在已有资料收集整理与总结的基础上，和全面的野外地质考察和样品采集，实验室内进行矿床学、岩相学、元素地球化学、同位素地球化学和水—岩反应等方面的实验测试分析，结合区域构造演化、成岩成矿时代等资料，探讨黔西南地区卡林型金矿床的成矿模式，主要取得以下成果和认识：（1）水银洞金矿床主要赋金地层为三叠系下统龙潭组第一二段和构造蚀变体（Sbt），岩性为粘土质粉砂岩、砂质粘土岩、生物碎屑灰岩、硅质岩、硅化灰岩和硅化粘土岩等；泥堡金矿床矿体主要赋存在龙潭组第一二段、Sbt和F1断层破碎带中，岩性为生物碎屑灰岩、粉砂岩、凝灰质次生石英岩、强硅化碳酸盐岩和断层角砾岩。两个金矿的围岩蚀变主要有硅化、碳酸盐化、黄铁矿化、毒砂化、粘土化、辉锑矿化和萤石化等，其中，硅化、碳酸盐化、黄铁矿化与金矿成矿有关，金矿产出部位均有上述蚀变特征。矿石矿物以含砷黄铁矿和毒砂为主，少量自然金、辉锑矿、辰砂、雄（雌）黄、硫砷铊汞矿和褐铁矿等；脉石矿物主要有石英、方解石、白云石和萤石等，少量绢云母、高岭石和有机质等。矿石结构有自形—半自形结构、环带状结构、网脉状结构、草莓状结构和假象结构等；矿石构造有块状构造、浸染状构造、网脉状构造、角砾状构造和条带状构造等。（2）水银洞和泥堡样品中含砷黄铁矿环带的Au含量明显高于核部Au含量，部分含砷黄铁矿核部Au含量也相对较高，大部分核部几乎不含Au，推测核部可能为成矿期早期黄铁矿或早期沉积成因黄铁矿。环带状黄铁矿核部与环带中Au含量高的位置对应的As含量也较高。毒砂Au含量相对含砷黄铁矿要低，一般认为是次要载金矿物。本次利用FE?SEM和EDS观察到了水银洞和泥堡金矿床中少量自然金颗粒，分布在早期砷含量较低或不含砷的黄铁矿边缘以及在细粒黄铁矿颗粒之间。因此，金主要有两种赋存状态：以价态金（Au+1）形式赋存于含砷黄铁矿结构；以自然金颗粒或包裹金（Au0）形式赋存于黄铁矿。（3）层控型矿体相对于围岩具有低Al2O3、高CaO、高MnO、高MgO、低TiO2、低K2O含量的特点；断控型矿体相对于围岩具有低SiO2、高CaO、高MnO、高MgO、低K2O、低Na2O、低P2O5含量的特点。层控型和断控型矿体相对于围岩均具有高Au、高As、高Hg和低Be含量的特点。水银洞金矿床的Sr、Ba元素亏损，Th、U、Ta等元素均富集。稀土元素总量（∑REE）较高，平均241.08 ppm，轻重稀土元素分馏较明显，LREE/HREE比值平均10.38，(La/Yb)N值平均13.40，δEu平均0.72，δCe平均0.85。在稀土元素球粒陨石标准化模式图上，具右倾平滑配分模式特征，左侧较陡，右侧较平缓。泥堡金矿床的Rb、Sr、Ba元素亏损，Th、U、Ta、Nd等元素均富集。稀土元素总量有三个区间范围，平均值分别为16.46 ppm、70.38 ppm、250.73 ppm，轻重稀土元素分馏较明显，LREE/HREE比值平均10.55，(La/Yb)N值平均12.72，δEu平均0.78，δCe平均1.06。在稀土元素球粒陨石标准化模式图上，具右倾平滑配分模式特征，左右两侧斜率相近。（4）水银洞和泥堡金矿成矿流体均具有中低温、低盐度、超高压的特点；成矿流体的碳氧同位素均具有海相碳酸盐岩碳和深部幔源（岩浆）碳混合来源的可能性；成矿流体的氢氧同位素均有混合流体（多来源）特征，即主要来自于深部岩浆水，流体在上升过程中，可能混入少量的变质水，在地壳浅部再混合部分大气水；两个金矿床的黄铁矿硫同位素组成具有还原硫和幔源硫（岩浆硫）的特征。（5）选择了高Au含量的水银洞金矿矿石样品作为本次水—岩反应实验的原样。样品重量为0.60 g，反应溶液为6.00 ml，溶液的盐度为6.0 wt.%NaCl或NaHCO3 equiv.，设计压力为15 MPa，温度设计为180 ℃、200 ℃、220 ℃、240 ℃，pH值设计为3、5，实验反应时间设计为48h、96h。从∑REE含量来看，单一变量为温度时（180℃、200℃、220℃、240℃），大致呈现温度越高溶液中∑REE含量越高、粉末中∑REE含量越低的趋势，即在一定温度范围内，温度越高，可能将有利于水—岩反应的进行；当单一变量为pH值时（pH=3、pH=5），pH=5相比pH=3，溶液中的∑REE含量较高，粉末中的∑REE含量较低，说明在pH=5的条件下，原样中的稀土元素更易迁移。当单一变量为温度（200℃、220℃、240℃）时，无论pH=3还是pH=5，随着温度的升高，溶液中Au含量均呈上升趋势。Au、Hg、Fe元素在NaCl盐溶液中的迁移量大于NaHCO3，As、Sb元素在NaCl中的迁移量小于NaHCO3，说明含NaCl盐溶液相对含有NaHCO3而言，更有利于Au、Hg和Fe元素的迁移，而溶液中含有NaHCO3，则有利于As、Sb元素的迁移。Au、Hg元素在有机酸和无机酸中的迁移程度相差不大；As、Sb元素在草酸、腐殖酸两种还原性有机酸中的迁移程度明显高于其他无机酸和中性有机酸；Fe元素在腐殖酸中的迁移量（481.75 ppm）明显大于第二位的柠檬酸（5.89 ppm）。（6）综合分析水银洞和泥堡金矿床的区域地质特征、动力学背景、矿床地质特征、成矿物质来源、成矿流体性质、主要控矿构造、蚀变矿化特征以及成矿演化过程，结合深部隐伏岩体资料，提出了以水银洞和泥堡金矿床为代表的卡林型金矿床成矿模式。在晚侏罗世—早白垩世时期（122～148 Ma），整个华南板块经历了大规模的岩石圈伸展作用，普遍发育褶皱和深大断裂构造，岩浆活动频繁。研究区深部岩浆演化分异形成的富含Au、As、Hg、Sb等的初始成矿流体沿早期构造通道向上运移，在运移过程中伴有浅部大气降水、少量变质水以及盆地流体等的加入，当运移至浅部的区域性构造不整合面、层间滑脱面以及断裂破碎带等主要控矿构造位置时，再与化学性质相对较活泼的不纯碳酸盐岩、火山碎屑岩、生物碎屑灰岩和砂屑灰岩等围岩发生水—岩反应，最后使得Au元素富集成矿。

Southwestern of Guizhou is an important part of the so-called "Golden Triangle" in Yunnan, Guizhou and Guangxi provinces, SW China for god deposits with many large and super-large Carlin-type gold deposits discovered, such as the Shuiyindong, Nibao, Lannigou and Yata etc. The marine sediments from the Cambrian to Middle Triassic periods, and continental sediments since the Late Triassic and the Devonian, Carboniferous, Permian and Triassic strata are well preserved. Among them, the marine sedimentary strata of Permian and Triassic are the most important gold-bearing strata in Carlin-type gold deposits. The structures are orogenic folds and faults which formed in Indosinian and Yanshanian epochs, mainly composed of compound folds, which are nearly EW-trending. The magmatic activity is weak, and the igneous rocks are rarely seen on the surface.The Carlin-type gold deposits in southwestern Guizhou can be divided into stratabound controlled, structurally controlled, and stratabound-structurally controlled, according to morphology and attitude of orebody, ore-controlling structure, and ore-hosting strata. The orebodies of stratabound controlled gold deposits occur in layers in space, and their attitudes are basically consistent with those of strata. The orebodies are controlled by stratabound slip structures and regional unconformities between Maokou Formation and Longtan Formation. The orebodies of structurally controlled gold deposits mainly occur in the main faults and their secondary faults, and their attitudes are controlled by high-angle pressure torsional faults. The orebodies of stratabound-structurally controlled gold deposits have both stratabound controlled and structurally controlled ore-controlling structures, such as Shuiyindong, Nibao, Bojitian, and Zimudan gold deposits.In this paper, the Shuiyindong and Nibao gold deposits are selected as the research objects, and the metallogenic model of Carlin-type gold deposits in southwestern Guizhou is discussed by summarizing the existing data and field geological investigation, as well as the study of mineralogy, lithofacies, element geochemistry, isotope geochemistry, and water-rock reaction. The main achievements and understandings of this paper are as follows.(1) The main gold-bearing strata of Shuiyindong gold deposit are the first and second member of Longtan Formation and structural alteration (Sbt), and the lithology is clayey siltstone, sandy claystone, bioclastic limestone, silicified limestone, and silicified claystone. The orebodies of Nibao gold deposit mainly occur in the first and second member of Longtan Formation, Sbt, and F1 fault fractured zone, and the lithology is bioclastic limestone, siltstone, tuffaceous secondary quartzite, strongly silicified carbonate rock, and fault breccia. The wall rock alterations of the two gold deposits are silicification, carbonation, pyritization, arsenization, claying, stibnite mineralization, and fluorination. Among them, silicification, carbonation, and pyritization are related to gold mineralization, and the occurrence of gold deposits have the above alteration characteristics. Ore minerals are mainly arsenic-bearing pyrite and arsenopyrite, with natural gold, stibnite, cinnabar, realgar, orpiment, limonite and so on; gangue minerals are quartz, calcite, dolomite, and fluorite, and a small amount of sericite, kaolinite, and organic matter. Ore structure includes automorphic-semi-automorphic structure, annular structure, vein structure, strawberry-like structure, and pseudomorphic structure; ore structure includes massive structure, disseminated structure, vein structure, breccia structure, and banded structure.(2) The Au content of arsenic-bearing pyrite annulus in Shuiyindong and Nibao samples is obviously higher than that in the core, some arsenic-bearing pyrites also have relatively high Au content in the core, but most of the core contains almost no Au. It is speculated that the core may be early main metallogenic epoch pyrite or early sedimentary pyrite. The As content in the core of annular pyrite corresponds to the location of high Au content in annular pyrite. Au content in arsenopyrite is lower than that in arsenic-bearing pyrite, and is generally considered as a minor gold-bearing mineral. A small amount of natural gold particles have been found by Fe?SEM and EDS, which distributed in the edge of pyrite with low or no arsenic content in the early stage and between fine-grained pyrite particles. Therefore, there are two main occurrence form of gold: gold (Au+1) occurs in arsenic-bearing pyrite structure, and gold (Au0) occurs in pyrite in the form of natural gold particles or encapsulated gold.(3) The orebodies of stratabound controlled have the characteristics of low Al2O3, TiO2, K2O, and high CaO, MnO, MgO contents relative to the wall rocks; the orebodies of structurally controlled have the characteristics of low SiO2, K2O, Na2O, P2O5, and high CaO, MnO, MgO contents relative to the wall rocks. The orebodies of stratabound and structurally controlled are both characterized by high Au, As, Hg, and low Be contents relative to the wall rocks.The Sr and Ba in the Shuiyindong gold deposit are depleted, the Th, U, and Ta are enriched. The total amount of rare earth elements (∑REE) is relatively high, with an average of 241.08 ppm. The fractionation of light and heavy rare earth elements is obvious. The average of LREE/HREE ratio is 10.38, (La/Yb)N value is 13.40, the average of δEu and δCe is 0.72 and 0.85, respectively. On the normalized model map of rare earth element chondrites, it has the characteristics of right-leaning smooth distribution pattern, steeper on the left and gentle on the right. Rb, Sr, and Ba are depleted, the Th, U, Ta, and Nd are enriched in Nibao gold deposit. There are three ranges of rare earth elements, the average values are 16.46 ppm, 70.38 ppm, and 250.73 ppm, respectively. The fractionation of light and heavy rare earth elements is obvious. The average of LREE/HREE ratio is 10.55, (La/Yb)N value is 12.72, the average of δEu and δCe is 0.78 and 1.06, respectively. On the normalized model map of rare earth element chondrites, it is characterized by a right-leaning smooth distribution pattern with similar slopes on the left and right sides.(4) The metallogenic fluids of Shuiyindong and Nibao gold deposits are characterized by low temperature, low salinity, and ultra-high pressure; the carbon and oxygen isotopes of the metallogenic fluids have the possibility of mixing marine carbonate rocks carbon and deep mantle source (magma) carbon; the hydrogen and oxygen isotopes of the metallogenic fluids have the characteristics of mixing fluids, that is, they mainly come from deep magmatic water, and the fluids are rising, it is possible to mix a small amount of metamorphic water, then re-mix atmospheric water in the shallow crust. The pyrite sulfur isotope compositions of the two gold deposits are characterized by reductive sulfur and mantle-derived sulfur (magmatic sulfur).(5) Selected the ore sample of the Shuiyindong gold deposit with high Au content as the sample of this water-rock reaction experiment. The weight of the sample is 0.60 g, the reaction solution is 6.00 ml, the salinity of the solution is 6.0 wt.% NaCl or NaHCO3 equiv., the design pressure is 15 MPa, the temperature is 180, 200, 220, and 240 C, the pH is 3 and 5, the experimental reaction time is 48 h and 96 h.From the view of ∑REE contents, when the single variable is temperature (180, 200, 220, 240 ℃), the trend is that the higher the temperature is, the higher the ∑REE contents in solution, and the lower the ∑REE contents in powder. In a certain range, the higher the temperature is, the more favorable the water-rock reaction is. When the single variable is pH value (pH=3, pH=5), the higher the ∑REE contents in solution is compared with pH=3. The high ∑REE contents in the powder is lower, which indicates that rare earth elements in the original sample are easier to migrate under the condition of pH=5. When the single variable is temperature (200, 220, 240℃), whether pH=3 or pH=5, the content of Au in solution increases with the increase of temperature.The migration of Au, Hg, and Fe in NaCl is greater than in NaHCO3, As and Sb in NaCl is less than in NaHCO3. This indicates that NaCl-containing solution is more conducive to the migration of Au, Hg, and Fe than NaHCO3-containing solution, while NaHCO3-containing solution is conducive to the migration of As and Sb elements.The migration of Au and Hg in organic acid and inorganic acid is not very different; As and Sb in oxalic acid and humic acid are obviously higher than other inorganic acids and neutral organic acids; Fe in humic acid migration amount (481.75 ppm) is significantly greater than that in the second citric acid (5.89 ppm).(6) The regional geological characteristics, dynamic background, geological characteristics, source of ore-forming materials, nature of ore-forming fluids, main ore-controlling structures, alteration and mineralization characteristics, and metallogenic evolution process are comprehensively analyzed, combined with the data of deep concealed rock body inferred by geophysical prospecting, the author put forward the metallogenic model of Carlin-type gold deposits represented by Shuiyindong and Nibao gold deposits.During the Late Jurassic-Early Cretaceous (122-148 Ma), the whole South China plate was experiencing large-scale lithospheric extension, with folds and deep faults widely developed and frequent magmatic activities. The initial ore-forming fluids rich in Au, As, Hg, and Sb formed by magmatic evolution and differentiation in the deep part of this area migrate upward along the early tectonic channel, accompanied by shallow meteoric precipitation, metamorphic water and basin fluids, when they migrate to the shallow regional tectonic unconformity surface, interlayer slip surface, and fracture zone, then the ore-forming fluids undergo water-rock reaction with the active wall rocks, such as impure carbonate rocks, pyroclastic rocks, bioclastic limestone, and sandy limestone, finally, the Au is enriched and mineralized.