【作者】 毛晓冬；

【导师】 黄思静；

【作者基本信息】 成都理工大学 ， 矿物学、岩石学、矿床学， 2003， 博士

【摘要】 继二十世纪八十年代在滇黔桂地区发现卡林型金矿后，九十年代广东长坑—富湾金、银矿床的发现，是我国在东南沿海该类型金矿床的首次重大突破。金矿体和银矿体都严格受控于石炭系下统梓门桥组（C₁z）和三叠系上统小坪组（T₃x）之间的层间构造破碎带，呈似层状或大透镜状分布。矿体走向北东东，倾向南南东，倾角30～50°，下部较缓（15～30°）。矿体与围岩界线清楚，其间常见数十米厚的糜棱岩带。伴随金、银矿化的围岩蚀变以硅化（形成多期石英和玉髓）、泥化（形成伊利石、地开石、少量高岭石）和硫化物化（形成黄铁矿、辉锑矿、雄黄、雌黄、闪锌矿和方铅矿）为主，其次是重晶石化、碳酸盐化和萤石化。金以次显微金（少量自然金）分布于黄铁矿、石英微裂隙或者它们的边缘或吸附于伊利石的边缘。银矿则以含硫盐和单硫化物（如辉银矿、螺状硫银矿）产出，并见少量的自然银。主要的含银矿物包括深红银矿、硫锑铅银矿、辉锑银矿、银黝铜矿、辉银矿，其次还有脆硫锑银矿、淡红银矿、硫锑铜银矿。 金矿具有微细粒浸染型金矿的显著特征，却与银矿共存在同一层间构造破碎蚀变带内，这一特征又非完全意义上的卡林型金矿。近十年国内许多矿床学家和地球化学家对该矿床分别从地层、岩石、矿物、矿床及地球化学等不同角度对矿床进行了诸多研究（杜均恩，等，1993，1996；南颐，1993；林毓川，等，1993；夏萍，等，1996；张生，等，1997，1998；梁华英，等，1998，2000；关康，等，1997；林建南，2000），相继提出了构造蚀变岩（杜均恩等，1993）、热水沉积（夏萍，等，1996）、热（卤）水溶滤（饶家光，等，1997）、热液交代（张生，等，1997）等不同成矿模式，但对于矿床上金、下银金银分离的原因讨论得却不多，而对于矿床的形成年代还存在一定分歧。 本文通过对金、银矿矿石及围岩的微量元素组成特征的分析，认为金、银矿床成矿物质来源不同：金可能来源于矿区周围的下石炭统梓门桥组地层，银则来源于粤西地区广泛分布的中-古元古代地层（云开杂岩）。 通过对金、银矿石矿物的硫同位素组成测试及前人大量资料的综合研究，系统讨论了金、银矿床δ ³⁴S特征。在δ ³⁴S分布图上：金矿δ ³⁴S的分布呈波浪式，说明硫源较复杂，银矿δ ³⁴S分布呈塔式，反映硫来源单一。运用平克尼一拉夫特法作出的△34 δ SStn-Py和△³⁴S_Sp-Gn对δ ³⁴S_A和δ ³⁴S_B关系图上，分别得到金矿和银矿成矿热液δ ³⁴S∑s为-1.0‰～+1.6‰和+0.8‰～+6.0‰，证明金矿硫来源以深源硫和有机还原成因硫（地层硫）为主，银矿硫源为无机还原成因硫，揭示出金、银矿床成矿物质硫来源上的一定差异。 测定的金、银矿石矿物铅同位素组成表明，矿石钳同位素组成变化幅度较大，在单阶段增长曲线图上均呈线性分布，金矿石拟合直线与μ=8.64的普通铅单阶段增长曲线相切，表明金矿石铅乃普通和放射成因的两阶段混合而成的异常铅，单阶段演化方程计算结果显2002年成都理工大学博士论文示，金矿石混合铅的正常端元在1048.IMa前已从它的放射性母体中（源区）分离出来，铅的来源最大的可能是云开地区老于1048.IMa的中元古代地层;按两阶段异常铅演化方程，给定假设的含异常铅矿物的结晶时间的可能范围（晚三叠世到古近纪）t:二227一23.3Ma，计算得到对应tl二1225.9¹357.IMa，也表明异常铅来源于中元古界，属两阶段演化的产物;银矿石铅同位素组成部分落在金矿石的铅异常直线上，说明银矿石异常铅是富’。了Pb的端元铅与金矿石的两阶段异常铅（普通铅和放射性异常铅）的不同比例混合铅，是三阶段演化的异常铅:铅同位素构造模式图反映金矿石铅的壳源性质，而银矿石铅则有壳慢混合源的特点。 金银矿床原生矿石可划分为三种基本类型:硅质矿石、钙硅质矿石和铝硅质矿石。似碧玉岩（j aspero记）构成了硅质矿石和钙硅质矿石，主要由次生石英、黄铁矿及少量重晶石、雄黄、雌黄、伊利石、地开石等组成，次生石英含量上一般为70%一90%，具典型热液交代和交代残余结构，普遍发育典型的构造岩的角砾状构造、碎裂构造、碎斑构造、微裂隙及孔洞构造，无沉积岩结构构造。含金银似碧玉岩主要由成矿过程中硅化作用形成，经显微镜下观察，其硅化作用在金矿化期可划分为四期，银矿化阶段为一期。含金银似碧玉岩稀土元素组成轻稀土较重稀土富集，球粒陨石标准化分布型式呈右倾斜式展布，Ce轻度负异常，几乎全部样品均为Eu负异常，与典型的热水沉积硅质岩显著的Ce负异常和Eu正异常截然不同，所以似碧玉岩非热水沉积作用和海水沉积作用产物，而是热液交代所致，说明金银矿床不是发生于海水与沉积物界面之间的热水沉积成因，也不是SEDEx型矿床，而是低温热液交代矿床。 长坑一富湾金、银矿床，上金、下银，彼此互不重叠、互不包容，分别构成独立的金矿体和银矿体。金矿具有微细浸染型金矿（miero一desseminated gold deposit）的特征，与银矿紧密共生，通常，卡林型金矿床中金、银含量比大于1，部分矿床还达到100:1，而长坑一富湾金银矿床却小于1，甚至达到1:10或l:100，使该矿床变得非常独特。为深入了解金银矿床成矿时代更多还原

【Abstract】 Changkeng-Fuwan large-scale gold and super-large silver deposits have been explored in Sanshui Mesozoic-Cenozoic sedimentary basin (about 50km southwest Guangzhou, Guangdong Province) in 1990s. Gold and silver orebodies independently occurred in the same field and yielded in one brecciated zone with alteration. The inter-formational tectonic belt directly controlled the orebodies, which was located between the strata of Zimenqiao_Fm. (C1z) of Lower Carboniferous and Xiaoping Fm. (T3x) of Upper Triassic. The tectonic belt was also the unconformable contact boundary of Lower Carboniferous and Upper Triassic. The orebodies of gold and silver approximate are bedded or big lens striking trends to NEE and dipping towards SSE with 30 to 50 degrees but 15 to 30 degrees in lower part. The boundary between orebodies and host rocks is quite clear which is characterized with several ten meters of mylonites. The silicification, clavization and sulfidization were the main alteration for the host rocks. The silicification formed several stages of quartz and chalcedony, calvization formed illite, dickite and minor kaolinite. Sulfidization formed pyrite, stibnite, realgar, orpiment, sphalerite and galena. The gold is mainly micro or sub-micro desseminated gold and distribute in the fissures of pyrite and quartz or their edges or surrounding illite. The silver occurred with sulfosalt and single sulfide such as argentite and acanthite and minor native silver. Most of the silver-bearing minerals include pyrargyrite, andorite, miargyrite, freibergite, argentite, and minor owyheeite, proustite, and polybasite.The gold orebody is apparently characterized with all the features of micro-desseminated Carlin-type gold deposit in Nevada of the U.S, but it occurs in the same ore field and one inter-bed tectonic brecciated zone with silver orebody related to the quartz veins rich in sphalerite and galena obviously, which makes it a little different from the real Carlin-type deposit. Recent 10 years, quite many Chinese economic geologists and geochemists researched on this special deposit in different aspects such as stratigraphy, petrology, mineralogy, and geochemistry. About the genesis of the ore deposits and the metallogenic model, several different ideals have been initiated to be tectonic alteration type (Du JE, Ma CH, Zhang GH, 1993), hot-water sedimentary deposit type (Xia P, Zhang H, Wang XZ, Cheng JP, 1996), hot brine lixiviation (Rao JG, Liu HQ, Yang SY, et al., 1997) and hydrothermal replacement (Zhang S, Li TJ, Wang LK, 1997a, 1997b). But no any mentioned about the separating reasons of the gold and silver if they were one deposit and formed by the same metallization, and some different isotopic ages have been dated and obtained as well.Focusing on the trace element geochemistry for the gold and silver orebodies and its hostrocks, also the background values of Au and Ag in regional stratigraphies, the paper concludes that the sources of Au are quite different from the Ag. Probably Au came from the stratum of Zimenqiao Fm., Some materials of silver ore was supplied by the regional Mesoproterozoic or Paleoproterozoic stratigraphies such as Yunkai Complex. According to the REE contents of orebodies and host rocks and its chondrite normalized distribution charts, the paper predicts that the mineralization or silicification was resulted from the hydrothermal replacement not related to the hydrothermal sedimentary deposition or the sedimentary exhalation.According to the analyzing results of sulfur isotope compositions of gold and silver deposits and a quantity of data of other geochemists, this paper focuses on the characters of 6 34S. The diagram of 8 34S shows that the 6 34S of the minerals (pyrite , stibnite) of gold deposit distributes as a wavy shape, and that of the minerals (sphalerite, galena) in silver deposit distributes as tower form. They indicate that the sources of sulfur are complicated for gold but simple for silver, respectively. By using the method which was promoted by D.M.Pinckney and T.A.Rafter (1972), the更多还原