云南武定迤纳厂铁-铜-金-稀土矿床成矿流体与成矿作用

Ore-forming fluid and metallogenesis of the Yinachang Fe-Cu-Au-REE deposit, Wuding, Yunan Province, China

武定迤纳厂铁-铜-金-稀土矿位于我国云南省中部,在大地位置上处于扬子板块西缘,康滇地轴云南段。其铁-稀土矿体主要以似层状、浸染状产出,铜金矿体以脉状、块状产于角砾岩内部和铁-稀土矿体内。根据围岩蚀变、矿物组合和矿化特征的差异,将其矿化作用划分为矿化前期、主矿化期和矿化后期三个成矿期,其中主成矿期又分为铁氧化物-稀土矿化阶段和硫化物-金矿化阶段。流体包裹体岩相学特征、成分特征、同位素特征等研究表明,矿化前期为富含碱质和挥发分的高氧化性岩浆,具有高温(500～600℃)高压(150～200MPa)的特点并发生了流体不混熔,从而分离出高温高钠的岩浆热液,与围岩发生钠化反应后富铁;主矿化期铁氧化物-稀土矿化阶段流体为中高温(170～550℃)中高压(75～155MPa),与围岩碳酸岩发生降压交代反应,导致铁质和稀土沉淀,并使碳酸岩脱水而演化为变质热液。主矿化期硫化物-金矿化阶段流体由岩浆热液变为变质热液,并与大气降水发生混合作用(均一温度120～360℃,压力31～112MPa),导致pH、Eh、fO2、fS等物理化学条件发生变化,流体中的铜、金不再以络合物的形式稳定与流体中,从而发生沉淀。至矿化后期,主要流体转化为单一低温(95～270℃)、低盐度(1.0%～17.9%NaCleqv)的低温大气降水,矿化结束。武定迤纳厂铁-铜-金-稀土矿在具有铁氧化物-铜-金(IOCG型)矿床的成矿环境、矿体特征、矿物组合、蚀变特征以及包裹体特征和流体演化成矿过程,属于滇中地区代表性IOCG矿床,具有重要的成矿理论和区域找矿意义。

The Yinachang Fe-Cu-Au-REE deposit locates in the central of Yunan Province, China, the southern of Kangdian axis, which comprises to the Yangtze block to the SW edge. Fe-REE ores occur as banded and/or disseminated replacements with in the breccia pipes, whereas Cu-Au ores occur predominantly as massive and veinlets within wallrocks and magnetite ores. According to differences in mineral association, ore structure, texture and wallrock alterations, we divide the ore-forming process into three stages： pre-mineralization stage, dominant mineralization stage and post-mineralization stage, and the dominant mineralization stage is comprised by magnetite-REE substage and sulfide-gold substage. Researches in microphysiography, composition and isotope of fluid inclusions suggest that fluids in pre-mineralization stage are high salinity magma, containing alkalic components and volatile phase, which formed in condition of high pressure （150～200MPa） and high temperature （500～600℃）. Immiscibility effect happens in these magma, breeding the magmatic hydrothermal （mid-high temperature 170～550℃, mid-high pressure 73～155MPa）, which caused the albitization of carbonate, and extract the Fe to the fluid. Replacement between magmatic hydrothermal and carbonaceous wallrock causing the precipitation of Fe and REE in the magnetite-REE substage, and the dehydration of wallrock produced the metamorphic hydrothermal for the aulfide-gold substage. Metamorphic hydrothermal mixed with meteoric water （120～360℃, 31～112MPa）, changed the physical and chemical conditions such as pH, Eh, fO2、fS, Cu, Au is no longer stable as clathrate in fluid, but precipitated as sulfide （Cu） and substance （Au）. In the stage of post-mineralization, with the depletion of metamorphic hydrothermal, dominant fluid became pure meteoric water with low temperature （95～270℃）, low salinity （1.0%～17.9%NaCleqv）. The Yinachang Fe-Cu-Au-REE deposit have many similarities with Iron Oxide Copper Gold （IOCG） deposit in geological background, mineral deposit, mineral association, fluid evolution and mineralization process. It could be concluded as a typical IOCG deposits in central Yunnan Province.