云南武定迤纳厂岩浆热液型铁-铜-金-稀土矿床流体特征研究

Study on Ore-Forming Fluid Characteristics of Yinachang Fe-Cu-Au-REE Deposit, Wuding, Yunnan Province, China

武定迤纳厂铁-铜-金-稀土矿位于我国云南省中部,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岩浆气液期、交代成矿期、热液成矿期和成矿后热液期4个期次。根据流体包裹体岩相学特征、成分特征、同位素特征等研究表明,岩浆气液期流体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,从而分离出交代成矿期岩浆流体。交代成矿期流体温度为中高温(170～550℃),压力为75～155MPa,与围岩碳酸岩发生交代反应,导致铁质和稀土沉淀,并使碳酸岩脱水而演化为变质热液。热液成矿期流体由岩浆流体变为变质流体,并与大气降水发生混合作用(均一温度为120～360℃,压力为31～112MPa),导致物理化学条件发生变化,流体中的Cu、Au不再以络合物的形式稳定于流体中,而是发生沉淀。至成矿期后,主要流体转化为单一低温(95～270℃)、低盐度(1.0%～17.9%)的低温大气降水。

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 wallroeks and magnetite ores. According to differences in mineral association, ore structure＆texture and wallrock alterations, we divide the ore-forming process into four stages： Mag- ma stage, metasomatism mineralization stage, hydrothermal mineralization stage and post-mineralization stage. Researches in microphysiography, composition and isotope of fluid inclusions suggest that fluids in magma stage are high salinity fluids, containing alkalic components and volatile phase, which formed in condition of high pressure （150-200 MPa） and high temperature （500-600 ℃） . Immiscibility effect hap- pens in these fluids, breeding the magmatic hydrothermal （mid-high temperaturelT0-550℃, mid-high pressure73-155 MPa） in metasomatism mineralization stage. Replacement between magmatic hydrother- mal and carbonaceous wallrock causing the precipitation of Fe and REE, while the dehydration of wallrock produced the metamorphic hydrothermal of hydrothermal mineralization stage. Metamorphic hydrothermal mixed with meteoric water （120-360 ℃, 31-112 MPa）, changed the physical＆chemical conditions, 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%NaC1） . The characteris- tics of fluid inclusions in Yinachang Fe-Cu-Au-REE deposit have many similarities with IOCG deposits, combined with researches in other aspects, it could be concluded as a typical IOCG deposits in central Yun- nan province, has important significance in metallogenesis and prospecting.