广西大瑶山地区斑岩型铜钨钼金矿床成矿机制探讨

Metallogenic mechanism of porphyry copper-tungsten-molybdenum-gold deposits in Dayaoshan area

广西大瑶山地区近年来地质找矿获得较大进展,为评价其找矿前景,进行了斑岩型铜钨钼金矿床成矿机制探讨,并建立综合成矿模式。分别采集了燕山期大黎斑岩型钼矿床、圆珠顶斑岩型铜钼矿床和加里东期新坪斑岩型钨金矿床成矿围岩、矿体样品进行稀土元素分析,配分法显示斑岩型矿床(La/Yb)_N为10.83~12.89、δEu 0.60~0.73、δCe 0.97~0.98,类似于壳幔混源型岩浆特点;硫同位素组成显示δ^(34)S为-1.32‰~2.17‰,具有相应侵入岩体δ^(34)S值变化特征;氢氧同位素δ^(18)O值3.5‰~7.59‰,δD值-42‰^-57‰,投影点以岩浆水区域为主,变质水区域次之,据此推断斑岩型铜钨钼金矿床成矿物质大部分来源于岩体,少部分来源于寒武系或更老地层。典型矿床成矿元素迁移与沉淀环境分析认为,斑岩型矿床是成矿岩体多期侵入、成矿热液多次叠加作用结果,矿化类型取决于岩体性质、元素丰度值;建立了综合成矿模式:以斑岩型矿床为中心,往两侧依次分布着破碎带蚀变岩型矿床和石英脉型矿床,3种不同类型矿床具有物质成分同源性和矿物组合空间梯度性。

In Dayaoshan area,the mineralization-materials of porphyry deposits were mostly found from intrusive-granite,less extracted from Cambrian or Precambrian strata based on data analysis of REE,S-isotope and H- O isotope. The first evidence of REE in porphyry deposit was characteristic of crust-mantle mixed-source by value of（ La / Yb）_N= 10. 83- 12. 89,δEu = 0. 60- 0. 73 and δCe = 0. 97- 0. 98. The second evidence of sulfur isotope in porphyry deposit was characteristic of intrusive rock related to mineralization by value of δ^（34）S for- 1. 32‰ to 2. 17‰. The third evidence of hydrogen and oxygen isotope in porphyry deposit suggesting ore-fluid came mainly from intrusive rock,less from metamorphic rock by values of δ^（18）O,which range from 3. 5‰ to7. 59‰,δD which range from- 42‰ to- 57‰. Meanwhile,two conclusions were obtained by established mineralization-model based on environment analysis of migration and precipitation in ore-forming elements. The first conclusion is that concentration of ore-forming elements in minerogenesis resulted from intrusion of ore-forming magma-granite and superimposition of ore-forming fluid many times. The second conclusion is that the spatial organization of deposit can be divided into porphyry type located in the center,fracture alteration-rock type located in periphery,and quartz-vein type located in farther periphery. But all the characteristics are of material-composition homologous and mineral-assemblage space-gradient.