广西贵港六梅金矿的成因类型及找矿意义

Genetic Types and Prospecting Significance of Liumei Gold Deposit,Guigang,Guangxi Province,China

六梅金矿床位于广西贵港市大平天山岩体东北部,矿体赋存于寒武系黄洞口组细碎屑岩中,受高角度断裂构造的控制。根据矿物组合与脉体的切割关系,将矿床热液活动过程划分为4个阶段:石英—黄铁矿阶段(Ⅰ),黄铁矿—毒砂—石英阶段(Ⅱ),方铅矿—闪锌矿—黄铜矿—(砷)黝铜矿—铁白云石—石英阶段(Ⅲ),石英—铁白云石阶段(Ⅳ),其中Ⅱ阶段为主要的成矿阶段。载金矿物主要为毒砂和(砷)黄铁矿,EPMA分析结果显示金主要以“不可见”的次显微—超次显微包体金形式存在。流体包裹体测试结果表明:石英或方解石中的包裹体以气液两相为主,主成矿阶段温度平均为181℃,平均盐度[w(NaCl)]为9.36%,密度为0.946 g/cm3,显示成矿流体为低温、低盐度、低密度流体。H、O同位素组成(δD值介于-73‰^-57‰之间,δ18OH2O值介于2.3‰~6.1‰之间)显示成矿流体与岩浆热液有关,且后期有大气降水混入;载金硫化物δ34SV-CDT值介于-0.8‰~0.5‰之间,指示成矿物质来源于岩浆。上述特征表明六梅金矿与典型的卡林型金矿有较大区别,特别是缺乏卡林型金矿特有的低温矿物组合(雌黄—雄黄—辰砂),相反却含有较多的贱金属矿物(方铅矿—闪锌矿—黄铜矿),更接近于与岩浆活动有关的远端低温热液矿床。结合区域上矿床和岩体的空间分布特征,提出了(次火山岩)斑岩型金矿(龙头山金矿)—矽卡岩型银铅锌矿(头闸银铅锌矿)—远端低温热液型金矿(六梅金矿)的大平天山岩浆热液系统成矿模式。该模式暗示着六梅金矿往深部及向大平天山岩体方向应该存在中温热液脉状和矽卡岩型银铅锌矿床。该文建立的岩浆热液成矿系统模型对大瑶山地区类似矿床的找矿具有重要指导意义。

Liumei gold deposit is located in the northeast of Dapingtianshan stock,Guigang,Guangxi Province.According to mineral composition and pulse cutting relation,the deposit hydrothermal activity process is divided into four stages:(1)quartz-pyrite stage;(2)pyrite arsenopyrite-quartz stage;(3)galena-sphaleritechalcopyrite-tennantite-ankerite-quartz stage;(4)quartz-ankerite stage.The second stage as the main metallogenic stage.The main gold carriers are arsenopyrite and pyrite.EPMA analysis shows that Au mainly exists in the form of“invisible”submicroscopic-supermicroscopic inclusion gold.Fluid inclusion test shows that the inclusions in quartz or calcite are mainly gas-liquid two-phase,the average temperature in the main metallogenic stage is about 181℃,the average salinityw(NaCl)]is 9.36%,and the density is 0.946 g/cm3,indicating that the ore-forming fluid is low-temperature,low-salinity,low-density fluid.The hydrogen and oxygen isotopic composition(δD value between-73‰^-57‰,δ18OH2 O value between 2.3‰~6.1‰)indicates that the ore-forming fluid may be related to the magmatic hydrothermal fluid and was mixed by meteoric precipitation in the later period.The value of the gold-bearingδ34S is between-0.8‰and 0.5‰,indicating that the ore-forming material comes from magmatic rock.These features indicate that Liumei gold deposit is very different from typical carlin-type gold deposits,especially it is lack of characteristic of the low temperature carlin-type gold mineral combination(orpiment-realgar-cinnabar),but instead contain more base metals mineral galena-sphalerite-chalcopyrite),so it is closer to related to magmatic activities of distal low temperature hydrothermal deposit.Based on the spatial distribution characteristics of regional ore deposits and rock masses,the metallogenic model of Dapingtianshan magmatic hydrothermal system for porphyry gold and copper deposits(Longtoushan gold deposit),skarn-type silver lead and zinc deposits(Touzha Ag-Pb-Zn deposit)and distal low temperature hydrothermal gold deposits(Liumei gold deposit)is proposed.The model implies that there should be intermediate temperate hydrothermal vein and skarn type silver-lead-zinc deposits deep in Liumei gold deposit and in the direction of Dapingtianshan rock mass.The model of magmatic hydrothermal metallogenic system established in this paper has important guiding significance for similar ore deposits in Dayaoshan area.