高盐度、高温和高成矿金属的岩浆成矿流体——以格拉斯伯格Cu-Au矿为例

High temperature, salinity and high concentrated ore metal magmatic fluids: an example from Grasberg Cu-Au porphyry deposit.

印度尼西亚格拉斯伯格 Cu- Au矿是与斑状的石英二长岩体有关的斑岩矿床 ,石英二长岩遭受了以钾化为主的伴随有绢云母化和磁铁矿化的蚀变。 Cu- Au矿化可分为网脉型和浸染型 ,以前者为主 ,含金的黄铜矿石英脉切穿了岩体和钾化蚀变带。本次研究中见到四类包裹体 ,即岩浆包裹体、含子矿物包裹体、气体包裹体和液体包裹体 ,与矿化有关的是含子矿物包裹体和气体包裹体。这两类包裹体的均一温度从 40 0℃到 >70 0℃ ,含子矿物包裹体的盐度 6 0～ 78wt% Na Cl。这两类包裹体常共存 ,并且其均一温度十分相似 ,说明成矿流体经历了沸腾的阶段。黄铜矿作为子矿物出现 ,并且从含子矿物包裹体的 X萤光光谱的分析结果发现有 Cu、Pb、Zn和 Mn等金属元素存在 ,说明格拉斯伯格 Cu- Au斑岩矿床的成矿流体是高盐度。

The Grasberg Cu Au porphyry system is centered around multiple quartz monzodiorite composite stocks. There are several alterations including potassic alteration, sericitization and magnetitization. The mineralization could be divided into disseminated and network types. Field relationships show that the chalcopyrite quartz vein and veinlets are the major mineralization and cut K silicate alteration. Four types of fluid inclusions: magmatic, daughter mineral bearing, gas rich and liquid inclusions have been found, and the daughter mineral bearing and gas rich inclusions are found in quartz of chalcopyrite quartz veinlets. The temperature of homogenization of fluid inclusions ranges from 400 to over 700℃ and with high salinity from 60~78 wt% NaCl equivalent in daughter minerals bearing ones. Besides these, ore metals such as Cu, Pb, Zn and Mn have been found in fluid inclusions by petrography and synchrotron X ray fluorescence analyses. Boiling is an important factor during the mineralisation which is provided by the coexisting daughter mineral bearing and gas rich inclusions, and their similar homogenization temperatures. The evidences from this study and the isotopic research suggest that the ore forming fluids of Grasberg Cu Au porphyry deposit are magmatic in origin.