湖南柿竹园钨锡多金属矿田野鸡尾矿床同位素地球化学研究

Isotope geochemistry of the Yejiwei deposit in the Shizhuyuan W-Sn ore field in Hunan province.

湖南柿竹园钨锡多金属矿田野鸡尾矿床产于千里山花岗岩岩体东南缘与泥盆系中统棋梓桥组和泥盆系上统佘田桥组灰岩接触带附近。是一个富含钨、锡、铅锌等多种金属的矽卡岩-云英岩-硫化物复合型矿床,在空间上具有明显的分带现象。研究表明,该矿床中花岗岩造岩矿物的ε^(18)O 值在-1.7‰～+12.1‰之间,其中石英的δ^(18)O 值较高,变化范围为8.4‰～12.1‰,钾长石为3.8‰～8.6‰,黑云母为-1.7‰～-1.4‰。石英-钾长石和钾长石-黑云母矿物对的氧同位素平衡温度为350℃～630℃,低于一般花岗岩的结晶温度。石英包裹体的δD为-56‰～-62‰,位于正常岩浆水的范围之内。矽卡岩期流体的δ^(18)OH_2O 为8.2‰～9.2‰,δD为-100‰～-156‰;云英岩流体的δ^(18)O_(H_2O)为4.9‰～6.7%e,δD为-69‰;硫化物期流体的δ^(18)O_(H_2O)为2.5‰～-36.1‰,δD为-54‰;晚期石英脉流体的δ^(18)O_(H_2O)为-7.3‰,δD为-58‰。从矽卡岩到晚期石英脉,成矿流体的氢氧同位素组成具有独特的演化特征,可以用沸腾去气作用和岩浆水与雨水混合作用来解释。矿区围岩灰岩和大理岩的占δ^(18)O_(SMOW)值为4.2‰～20.0‰,δ^(13)C_(PDB)为-6.0‰～0.3‰,灰岩与大理岩的δ^(18)O 和δ^(13)C 显著不同,用矿化和蚀变过程中水-岩相互作用和同位素交换反应可以圆满地解释。矿床硫化物的δ^(34)S 值为+2.8‰～+8.9‰,其中矽卡岩硫化物的δ^(34)S 在+2.8‰～+8.9‰之间;云英岩中硫化物δ^(34)S 在+3.4‰～+6.9‰之间;硫化物阶段的δ^(34)S 在+3.7‰～+6.3‰之间。估算的成矿流体总硫δ^(34)S_(∑S)约为3‰,表明硫的主要来源可能来自千里山花岗岩岩浆。综合氢氧碳硫同位素组成研究,本文认为野鸡尾矿床成矿物质主要来自千里山花岗岩,也可能有少部分物质来源于围岩沉积岩。

The Yejiwei deposit from the Shizhuyuan W-Sn ore field in Hunan province occurs in the contact zone between the southeastern edge of the Qianlishan granite and the limestone of the Middle Devonian Qizixiao Group and Upper Devonian Setianqiao Group. This deposit consists of various types of W-Sn-Pb-Zn ores including skarn, greisen, and sulfide mineralization, with clear space distributions. The δ^18O values in granite minerals show an overall range from - 1.7‰ to ＋ 12. 1‰, in which the quartz has higher σ^18 O values （ 8. 4‰ to 12. 2‰） than those of K-feldspar （3. 8‰ to 8.6‰） and biotite （ - 1.7‰ to - 1.4‰）, The calculated mineral oxygen isotope equilibrium temperatures （350℃ to 630℃ ） are lower than the crystallization temperature of the granite. The 8D values of fluid inclusions in granite quartz vary from - 56‰ to - 62‰, which are within the normal magmatic water field. In skarn ores, the calculated fluid δ^18OH2O values range from 8.2‰ to 9.2‰ and the δD values are between - 100‰ and - 156‰. In greisen ores, the calculated fluid δ^18 OH2O values range from 4.9‰ to 6.7‰, and the δD value is - 69‰. During sulfide mineralization stage, the calculated fluid δ^18OH2O values range from 2.5‰ to -6. 1‰, and the δD value is - 54.2‰. In the latest stage of quartz veins, the calculated fluid δ^18 OH2O Value is -7.3‰ and the δD value is -57.7‰. The oxygen and hydrogen isotope variations from the early skarn ore stage to late quartz vein stage can be better explained by fluid degassing and fluid mixing between magmatic fluids and meteoric water. The host rocks of limestone and marble show δ^18 O values of 4.2‰ to 20.0‰, and δ^18 CPDB values of - 6. 0‰ to 0.3‰. This large isotopic variation can be better explained by fluid-rock interaction and isotope exchange during mineralization and alteration. The sulfide minerals in the deposit show a total δ^34S variation from ＋ 2.8‰to ＋ 8.9‰. In the skarn ores, the 6Z4S values are ＋ 2.8‰ to ＋ 8.9‰, whereas in the greisen ores the δ^14 S values show a narrower range from ＋ 3.4‰ to ＋ 6. 9‰, In the sulfide mineralization stage, the δ^334S values vary from ＋3.7‰ to ＋6.3‰. The value of δ^14S∑s is estimated to be -3‰, suggesting that the sulfur may mainly come from the Qianlishan granite magma. We suggest that the ore material sources of the Yejiwei deposit largely derived from the Qianlishan granite, but minor proportion may also come from the host sedimentary rocks.