湘中龙山Au-Sb矿床成矿物质来源——来自S、Pb和Sr同位素证据

Constraints on the ore-forming source material of the Longshan Au-Sb deposit in central Hunan: evidence from S, Pb and Sr isotopes

龙山Au-Sb矿床是湘中Au、Sb矿集区的代表性矿床,本文对其不同类型矿石、矿区围岩和区域地层进行了S、Pb、Sr同位素组成对比研究。矿石中硫化物的δ34S值为-3.0‰~5.1‰,平均值2.3‰;矿区围岩的δ34S值为4.0‰~5.9‰,平均值5.2‰;区域地层的δ34S值为9.3‰~13.3‰,平均值11.3‰。矿石与矿区围岩、区域地层的硫同位素组成差别较大,矿石硫具岩浆来源特征。矿石中硫化物的206Pb/204Pb、207Pb/204Pb和208Pb/204Pb比值分别为16.992~18.457、15.392~15.722和37.586~38.960,矿区围岩的206Pb/204Pb、207Pb/204Pb和208Pb/204Pb比值分别为17.630~17.993、15.522~15.644和37.981~38.366;区域地层的206Pb/204Pb、207Pb/204Pb和208Pb/204Pb比值分别为17.566~18.092、15.430~15.630和37.988~38.710。矿石铅同位素组成变化较大,矿石铅的来源较复杂,赋矿地层、印支期岩浆岩和上地幔可能都为其提供了部分铅。石英流体包裹体的(87Sr/86Sr)i比值为0.71540~0.72309,矿区围岩的(87Sr/86Sr)i比值为0.71844~0.72153,区域地层的(87Sr/86Sr)i比值为0.71792~0.71939,矿石、矿区围岩、区域地层的初始锶同位素值均较高,主要为壳源锶,部分锶来自赋矿地层,部分来自印支期岩浆岩。龙山矿床成矿物质具壳幔混合来源特征,矿化剂硫主要来源于岩浆,成矿物质部分来自江口组地层,部分来自印支期岩浆岩。

The Longshan Au-Sb deposit is a typical Au-Sb ore deposit in central Hunan. Analysis and comparison of S, Pb and Sr isotopic composition of different ores, wall rocks and regional strata from the Longshan deposit have been carried out in this study. The δ34S values of ores vary from-3.0‰ to 5.1‰ with an average of 2.3‰ and the δ34S values of wall rocks vary from 4.0‰ to 5.9‰ with an average of 5.2‰, and the δ34S value of the regional strata from 9.3 ‰ to 13.3‰ with the average of 11.3‰. The sulfur isotopic compositions of ores differ from the wall rocks and the regional strata, and show magmatic character. The 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of ores are 16.992~18.457, 15.392~15.722 and 37.586~38.960, respectively;the 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of wall rocks are 17.630~17.993, 15.522~15.644, 38.981~38.366, respectively;and the 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of regional strata are 17.566~18.092, 15.430~15.630 and 37.988~38.710, respectively. The Pb isotopic compositions of ores vary greatly, and the sources are complicated, where the strata, Indosinian magma and upper mantle are all possible lead providers. The(87Sr/86Sr)i range of fluid inclusions in quartz is 0.71540~0.72309, the(87Sr/86Sr)i range of wall rocks is 0.71844~0.72153;the(87Sr/86Sr)i range of regional strata is 0.71792~0.71939. The initial Sr values of ore rocks, wall rocks and regional strata are all relatively high, suggesting that they might mainly have come from the crust, with some contribution of Sr from ore-bearing strata and the Indosinian magma. The ore-forming materials in the Longshan deposits show characteristics of crust-mantle mixture, in which the ore-forming sulfur originated from magma while the other ore-forming material are partially from the regional strata of the Jiangkou Formation, and partially from the Indosinian magma.