滇西老厂隐伏斑岩-矽卡岩型钼矿床成矿过程与物质来源  

Metallization process and metallogenic sources of concealed porphyry-skarn Mo deposit,Laochang,western Yunnan

作　　者：黄钰涵[1] 邓军[1] 李龚健[1] 蒙福清 毛富祥 张鹏飞[1] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,北京100083 [2]云南澜沧铅矿有限公司,澜沧665601

出　　处：《岩石学报》2017年第7期2099-2114,共16页Acta Petrologica Sinica

基　　金：国家重点基础研究发展计划"973"项目(2015CB452606;2009CB421008);国家重点研发计划(2016YFC0600307);国家自然科学青年基金项目(41602090)联合资助

摘　　要：滇西老厂新生代隐伏斑岩-矽卡岩矿床位于西南三江特提斯南段昌宁-缝合带内,是缝合带内目前发现唯一的钼矿床。前人的研究主要围绕新生代岩体展开,而对于有关的斑岩-矽卡岩成矿作用的研究尚待深化。本文对老厂斑岩-矽卡岩型钼矿床进行了岩相学、电子探针和硫同位素分析,探讨成矿物理化学条件和物质来源。斑岩型矿床成矿过程包括成岩期、钾化期与硅化期,矽卡岩型成矿过程包括进矽卡岩期、早退矽卡岩期和晚退矽卡岩期。斑岩与矽卡岩最终都经历了低温热液的改造。矿物学和电子探针分析表明:角闪石结晶温度为730~790℃,氧逸度NNO+1.6~2.5,成岩阶段具有高温和相对还原的特点;钾化及硅化阶段黑云母结晶温度从650℃逐步降低为450℃,然而相应的氧逸度由QMF+1.9升高为QMF+2.5。斑岩内辉钼矿的富集以及矽卡岩内金属硫化物的沉积,均与温度下降和氧逸度升高关系密切。已知斑岩全岩δ^(34)SVCDT(+3.00‰^+11.00‰)与无矿化斑岩全岩δ^(34)S组成一致,表明成矿物质主要来源于岩浆。金属硫化物δ^(34)SVCDT(-1.96‰^+1.99‰)组成与低氧逸度斑岩矿床的δ34S组成特征符合。本文为老厂钼矿床成矿机制提出了客观合理的解释,为丰富西南三江特提斯新生代斑岩-矽卡岩成矿系统的研究提供了新的参考。Laochang concealed Cenozoic porphyry-skarn deposit has recently been reported as a unique Mo-dominant deposit in southern Sanjiang Tethyan orogenic belt,SW China. Previous studies were mainly focused on the petrogenesis of the porphyry,but the studies on the porphyry-skarn deposit have been rarely reported. In this paper,the petrology,EPMA and S-isotope experiments on Laochang porphyry-skarn Mo deposit were conducted to analyze the metallization process and materials sources. The metallization sequence of porphyry can be divided into diagenesis,potassic alteration and silicification stages. Sequence of skarn can identified as prograde,early-retrograde and late-retrograde stages. Porphyry and skarn are both altered in hydrothermal stage. Mineralogy and EPMA analysis show amphibole thermometer have crystallization temperature at 730 - 790℃ with oxygen fugacity（ fO_2） at NNO ＋ 1. 6- 2. 5,which proves diagenesis stage was hyperthermal and relatively reduced. Biotite thermometer in potassic alteration and silicification stage show porphyry cooling from 650℃ to 450℃,oxygen fugacity rising from QMF ＋ 1. 9 to QMF ＋ 2. 5. Gathering of molybdenite in porphyry and precipitation of sulfide in skarn have strong connection to decreasing temperature and increasing oxygen fugacity. Ore body δ34SVCDT（ ＋ 3. 00‰ - ＋ 11. 00‰） are consistent with none-alternation porphyry,show inheritance directly from initial magma. Sulfides δ34SVCDT（-1. 96‰ to ＋ 1. 99‰） are coincidence with δ34S in porphyry deposits of low oxygen fugacity. This research gives objective and reasonable explanation on metallization mechanism of Laochang Mo-deposit,and provide example for Cenozoic porphyry-skarn system in Sanjiang Tethys.

关 键 词：老厂 斑岩-矽卡岩型钼矿床 结晶温度 氧逸度 成矿过程 物质来源 

分 类 号：P618.65[天文地球—矿床学]