滇西南澜沧江带官房铜矿矿床成因和成矿模式探讨

GENESIS AND METALLOGENIC MODEL FOR GUANFANG COPPER DEPOSIT IN SOUTH LANCANGJIANG BELT, WESTERN YUNNAN PROVINCE

官房铜矿是南澜沧江构造岩浆带正在勘探的规模较大的铜矿床,本文归纳整理了该矿床的地质特征,并结合微量元素和稳定同位素,对矿床成因、成矿模式进行了初步探讨,指出了区域找矿的方向。铜矿化主要与硅化和黄铁矿化有关,含矿岩石为上三叠统小定西组富钾基性火山岩,其稀土元素表现为轻稀土富集型,无或弱的负Eu异常;微量元素配分型式以K、Rb、Ba、Th强烈富集,Ti、Y、Yb、Cr明显亏损为特征,与石英脉型铜矿石存在明显的差异。矿体严格受放射状断裂和岩性双重控制。矿石硫同位素组成稳定,δ34SV-CDT变化范围为-11.88‰～-5.67‰,主要为深源硫。流体包裹体的成分和氢氧同位素组成表明成矿流体为大气降水和岩浆水的混合流体。地质和地球化学特征表明官房铜矿属浅成中-低温热液矿床,形成于相对开放的系统,成矿与隐伏岩体的岩浆作用有明显的成因联系。

The Guanfang copper deposit is a new prospecting ore deposit in the south Lancangjiang magma tectonic belt, Yunxian, Yunnan. In this paper, geological and geochemical characteristics of the ore deposit are studied in detail, and its genesis and material source and metallogenic model are discussed on the basis of trace elements, fluid inclusions and isotopes of the copper ores and ore-beating rocks. Copper mineralization is closely related to silicification and pyritization. The major oxides of basaltic volcanic rocks of Xiaodingxi Formation belong to high-potassium calc-alkali basalt -shoshonite series. The REE distribution pattern of the ore-beating rocks is slightly right - oblique in orientation, with an average ∑ REE of 173.81 ×10^-6 and the Eu element being non - or slightly negative - abnormal in terms of abundance, here the pattern is obviously different from that of the ore. In the primary mantle-normalized trace element distribution pattern diagram the ore-bearing rocks show enrichment of K, Rb, Ba, Th and depletion of Ti, Y, Yb, Cr, which is in conformity with the features of arc-volcanic rocks on the continental margin. The orebodies are strictly controlled by the faults that radiate toward the outside and the lithologic characters of the volcanic rocks. The sulfur isotope composition of the main sulfides is within the range of - 11.88‰～-5.67‰ δ^34Sv-CDT. Oxygen and hydrogen isotopic analyses and characteristics of inclusions indicate that the oreforming fluid of the ore deposit is of hybrid type that is composed of magma water and meteoric water. Geological and geochemical characteristics indicate that Guanfang copper deposit is hydrothermal Cu ore deposit that is of genetically low to medium Temperatureeratures and formed in a relatively open system and related to the magma activity of concealed rock bodies, with ore-forming materials being derived from the lower crust and upper mantle.