摘要
湖南黄沙坪W-Mo-Bi-Pb-Zn多金属矿床规模大、矿种多、范围小、分带明显,是南岭有色金属成矿带的代表性矿床之一。成矿地质体为碱长花岗斑岩,与下石炭统灰岩接触带发生大规模矽卡岩化,形成大型钨、钼、铋、萤石以及铁的共生矿床。围绕矽卡岩向外,分布铜锌、铅锌、铅锌银的分带,对应的矿化组合分别为粗粒磁黄铁矿-闪锌矿-黄铜矿、中粗粒磁黄铁矿-闪锌矿-方铅矿、胶状黄铁矿-闪锌矿-方铅矿。围绕花岗斑岩,硫化物矿物的δ34S值呈带状分布,其δ34S总体变化为2.3‰～17.5‰,花岗斑岩中浸染状辉钼矿δ34S为17.1‰,矽卡岩中硫化物δ34S>15‰,矽卡岩附近及外侧的铅锌矿体10‰<δ34S<15‰,外围的铅锌银矿体δ34S<10‰。下石炭统中代表沉积特点的细粒浸染状黄铁矿δ34S为-3.1‰～-22.6‰。铅同位素206Pb/204Pb为18.525～18.603,207Pb/204Pb为15.706～15.792,208Pb/204Pb为38.889～39.178。综合研究表明,黄沙坪矿床成矿物质硫和铅主要来自花岗斑岩。经硫同位素热力学平衡计算,引起δ34S值围绕花岗斑岩体分带的主要原因是随温度下降以及物理化学条件变化导致的热力学分馏作用,其次是沉积岩围岩中低δ34S值硫的加入。对南岭地区花岗岩、古生代地层等的δ34S值对比研究发现,引起花岗斑岩岩浆高δ34S值的主要原因是深部富含硫化物(δ34S值高)地层对富含挥发份(Li-F)的碱长花岗岩岩浆的混染作用,其次是成矿作用过程中地层与岩浆的相互作用(包括同化混染)。围绕黄沙坪矿床,湘南地区矽卡岩型钨多金属矿存在一个较高的δ34S值分布区。宝山矽卡岩型Cu-Mo-Pb-Zn矿床矿石硫化物δ34S为-1‰～3.6‰,206Pb/204Pb为18.602～18.672,207Pb/204Pb为15.693～15.780,208Pb/204Pb为38.901～39.186。因此,宝山矿床与黄沙坪矿床的物质来源和成矿机制不同,宝山矿床硫、铅同位素组成集中,分布范围不同于黄沙坪,成矿物质来自岩浆岩。黄沙坪、宝山矿床代表了南岭地区燕山早期存在两类不同性质的岩浆活动与成矿组合。
Huangshaping W-Mo-Bi-Pb-Zn polymetallic ore deposit,located at Yizhang County,Hunan Province,South China,is one of the most famous deposits in Nanling tungsten belt.This deposit shows characteristics of multiple elements mineralization,large ore reserve in a small area 1km2,and typical zonation from skarn-type mineralization to distal hydrothermal veins.The skarn mineralization of W,Mo,Bi and fluorite occurred at the contact zone between alkali feldspar granite-porphyry and the Lower Carboniferous limestone.The Cu-Zn,Pb-Zn and Pb-Zn-Ag sulfide ore bodies distribute from the skarn zone to distal limestone strata,and the mineral assemblage are coarse-grained pyrrhotite（Po）-sphalerite（Sp）-chalcopyrite（Cp）,Po-Sp-Galena（Ga）,and colloidal pyrite-Sp-Ga,respectively.The δ^34Svalues of the sulfide minerals are from 2.3‰ to 17.5‰,and a zonation of the δ^34Svalue is observed around the granite-porphyry.The δ^34Svalue of molybdenite disseminated at granite-porphyry is 17.1‰,the sulfide minerals from the skarn zone show δ^34Svalues 15‰,the lead-zinc orebodies near the skarn show δ^34Svalues between 10‰ and 15‰,and the distal Pb-Zn-Ag ore bodies form the limestone strata show δ^34Svalues 10‰.The disseminated pyrite in the Lower Carboniferous sediment rocks shows δ^34Svalues from-3.1‰ to-22.6‰.The lead isotopic compositions of the sulfide minerals are as following：206^Pb/204^Pb of 18.525-18.603,207Pb/204Pb of 15.706-15.792,and 208Pb/204Pb of 38.889-39.178.According to these results,it is suggested that the sulfur and lead of the Huangshaping deposit may have originally came from the granite-porphyry,but also with minor contributions from the limestone strata.The δ^34Szonation around the porphyry is probably caused by the thermodynamic isotope fractionation related to the temperature decreasing,varying of the redox conditions and pH values.Alternatively,it is also possible that some amounts of sulfur with lower δ^34Svalue may have also been derived from the Lower Carboniferous sedimentary rocks.The high δ^34Svalues in granite porphyry magma may have been caused by incorporation of the sulfides with high δ^34Svalues from the sedimentary rocks at depth（i.e.Devonian carbonate rocks） and by contamination of the carbonate wall rocks during ore-forming processes.The Baoshan Cu-Mo-Pb-Zn skarn deposit is located about 9km north of the Huangshaping deposit,the sulfide minerals from Baoshan show δ^34Svalues of-1‰ to 3.6‰,and 206^Pb/204^Pb of 18.602-18.672,207Pb/204Pb of 15.693-15.780,and 208Pb/204Pb of 38.901-39.186.The Baoshan Cu-Mo-Pb-Zn polymetallic ore deposit show different origin and mineralization mechanism from the Huangshaping deposit.The Bashan deposit has a very narrow range of sulfur and lead isotopic compositions,and the hydrothermal fluid should have derived mainly from the granodiorite-porphyry magma.Therefore,these two deposits may represent the two types of magmatic activity and mineralization at Late Jurassic period in Nanling region,South China.
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2012年第12期3809-3822,共14页
Acta Petrologica Sinica
基金
全国危机矿山接替资源找矿项目(20089927)
国家科技支撑课题(2011BAB04B08)联合资助
关键词
硫同位素
铅同位素
矿床成因
成矿机制
钨矿
铅锌矿
湖南省
Sulfur isotope
Lead isotope
Ore genesis
Tungsten deposit
Lead-zinc deposit
Skarn deposit
Hunan Province
