滇—黔边境鲁甸沿河铜矿床的发现与峨眉山大火成岩省找矿新思路

DISCOVERY OF YANHE COPPER DEPOSIT IN THE YUNNANGUIZHOU BORDER AREA AND A NEW TRAIN OF THOUGHT FOR COPPER PROSPECTING IN THE LARGE IGNEOUS PROVINCE OF EMEISHAN FLOOD BASALTS

滇—黔边境鲁甸沿河铜矿床矿化受二叠纪玄武岩最上部古火山口相角砾凝灰岩—气孔状熔岩和上覆宣威组碳泥质层控制。矿石矿物主要为自然铜、氧化铜与辉铜矿。自然铜呈板片状、网脉状、浸染状产出。矿化与阳起石化、沥青化、硅化和沸石化密切相关。在峨眉山大火成岩省寻找沿河式铜矿应关注以下重要问题:①地球化学急变带所确定的岩石圈不连续界面控制了峨眉山玄武岩裂隙式喷发;②古火山口相从苦橄质到安山质高分异岩浆喷发;③火山口环境联系下的贫硫、贫酸根同生热液活动;④富有机质地层中有机—无机相互作用所产生的强还原性环境;⑤脆韧性断裂带的发育导致矿体的进一步富化。

Copper mineralization of the Yanhe deposit in Ludian county near the border area between Yunnan and Guizhou provinces is related to the strata of tuff breccia, and vesicular lavaignimbrite beds in the ancient volcanic vents of the Emeishan flood basalts, as well as the Xuanwei Formation of Upper Permian composed of carbonaceous argillites and siliceous rocks. Ore minerals are manly native coppers, copper oxides, chalcocites and chalcopyrites. The native coppers shows occurrence in slabflaky, net veined and impregnated. Copper mineralization is tightly associated with zeolitization, actinolitetremolitization, bituminization and silicatization. These features are quite similar to those of the copper deposits in Keweenaw Peninsula, Michigan, USA. The key points for searching copper deposits with features of the Yanhe style in the large igneous province of the Emeishan basalts are:①discontinuous faces of lithosphere identified by geochemical steep zones of NW strike controlled rifting eruptions of the Emeishan basalts. ②magma eruptions with high fractionation from picritic to andesitic in magma chambers of vents.③synvolcanic hydrothermal activation depleted in sulfur and acid radicals in volcanic vent environments caused copper mineralization on large scale.④organicinorganic interaction within strata enriched in organic matter provided strong reduction environments for native copper formation.⑤brittletough faulting induced progressive copper enrichment in ores.