吉林红旗岭富家矿床矿石矿物化学和硫同位素特征——对铜镍硫化物矿床成因及成矿过程的约束

Mineral Chemistry and Sulfur Isotopic Characteristics of Ores from the Fujia Deposit in Hongqiling Area,Jilin Province:Constraints on the Genesis and Ore-forming Processes of Ni-Cu Sulfide Deposit

本文对吉林红旗岭富家矿床中的矿石矿物进行了系统的矿物化学和硫同位素研究。矿石矿物共生组合主要为磁黄铁矿(Po)-镍黄铁矿(Pn)-黄铜矿(Cp)-黄铁矿(Py),其中Po有单斜磁黄铁矿(Mpo)、六方磁黄铁矿(Hpo)和六方陨硫铁(Tr)相之分,并以Mpo(低温相)为主;Pn有Pn(1)→Pn(2)→Pn(3)的演化趋势;Py有Py(1)→Py(2)→Py(3)→Py(4),均为同一矿化期的不同世代的产物。利用Py-Po矿物对计算出矿石矿物的结晶温度介于500~300℃之间,大致结晶顺序为Pn→Po→Cp→Py。硫同位素特征表明,δ^(34)S值变化较小,介于–4.70‰^+2.40‰之间,δ^(34)S值呈塔式分布,集中分布于–2.5‰^+2.5‰之间,δ^(34)S值略高于地幔硫(0±2‰),并有δ^(34)S_(Po)>δ^(34)S_(硫化物)>δ^(34)S_(Py)的特征,表明硫来源于地幔,仅有微弱的地壳物质混染,且成矿熔体中硫已达到平衡。结合野外矿体特征和矿石组构特征,富家矿床的成矿物质来源于上地幔;成矿作用方式以岩浆熔离作用为主,兼具岩浆期后热液叠加成矿作用;矿床为通道式成矿,属于深部熔离-贯入式成因。

Systematic studies of mineral chemistry and sulfur isotope of the ore minerals were carried out at the Fujia deposit in Hongqiling area, Jilin Province. Coexisting ore minerals mainly consist of pyrrhotite （Po）, pentlandite （Pn）, chalcopyrite （Cp） and pyrite （Py）. The pyrrhotite includes monoclinic pyrrhotite （Mpo）, hexagonal pyrrhotite （Hpo） and troilite （Tr）, with the Mpo （a low temperature polymorphism） being dominant. The pentlandite evolved from Pn（1） via Pn（2） to Pn（3）, whereas the pyrite varied in the sequence of Py（1）→Py（2）→Py（3）→Py（4） at the same mineralization stage. The pyrite-pyrrhotite mineral thermometry shows that the mineralizing temperatures of the ore minerals vary between 500°C and 300°C, while the mineralizing sequence is approximately Pn→Po→Cp→Py. Sulfur isotopic characteristics show that the variation of δ34S values is relatively small （from –4.70‰ to ＋2.40‰）, and statistics of the values fit tower-style distribution between –2.5‰ and ＋2.5‰, which indicates that sulfur of metal sources of this deposit was derived from the mantle with only a slight crustal contamination. In addition, the δ34S values show δ34SPo〉δ34Ssulfide〉δ34Spy, indicating that sulfur reached equilibrium in ore-forming melt. In combination with characteristics of the orebodies in the field and ore fabric, the authors hold that the ore-forming materials were principally derived from the upper mantle. Magmatic liquation was the major mineralization process, combined with obvious magmatic hydrothermal superimposition. The deposit is conduit-type mineralization, which can be explained by intrusion of deep ore-bearing magma and magma liquation-conduit-style mineralization.