滇中郝家河砂岩铜矿的地球化学及其成因意义

GEOCHEMISTRY AND GENETIC SIGNIFICANCE OF THE HAOJ1AHE SANDSTONE-HOSTED COPPER DEPOSITS IN CENTRAL YUNNAN

本文论述了滇中中生代地层与矿区及其外围马头山组中铜的时空分布与迁移富集规律,揭示了矿床的沉积-后期叠加改造成因。成矿作用经历了同生沉积形成矿源层,后期叠加改造形成矿体的过程。后期改造中铜元素发生了大量迁移,矿质主要来自矿体之下伏紫色矿源层。

The Haojiahe copper deposit is located at the east edge of the Mesozoic faulted basin of central Yunnan. Ore bodies occur in the light-coloured sandstone at the upper part of the violet beds of the Haojiahe Member of the Upper Cretaceous-Matoushan Formation.The weathered products of the pre-Sinian copper-bearing volcano-sedimento-metamorphic formation on the Kangdian old land the eastern side of the basin, appears to be the prodominant source of the Mesozoic copper-bearing formation. Probably owing to continuous uplift of the Ailao Mountains after the Indosinian movement, the sedimentary basin moved successively from west to east and ore source materials from the old land in the east might have increased) therefore, the copper abundance in the Mesozoic strata simultaneously might increase also from west to east and from bottom to top. The sedimentation of the lower member of the Matoushan Formation may recur immediately after folding movements and lengthy sedimentary gaps. As the sediment source from the eastern old land would have been subjected to prolonged weathering and enrichment of copper protore could proceeded more thoroughly, the copper content in the Matoushan Formation around the mining area increases from top to bottom and its average value is 1-5 times as high as that in the same formation of the region (western). This is the main cause why sandstone-hosted copper deposits in central Yunnan are concentrated in the Matoushan Formation at the east edge of the basin.As compared with the areas outside of the mining area, the copper content of the violet beds is lower and that of the light-coloured beds is higher. Trend surface analysis of the copper content in the violet beds shows an extensive low-Cu content area below the SW side of the orebody swarm, implying that copper in the violet beds have migrated upward and deposited as ores. According to the deposit zoning pattern it appears that the ore-bearing hydrothennal solutions should generally flow from south to north and from below upward. The greatest E-W-trending fault F1 in the mining area may have served as a passageway, for flow of ore fluids.Calculation of the copper content suggests that the copper removed from the violet beds in the mining area accounts for about 50% of the available copper reserves. The above calculation result coupled with other data indicates that oart of copper was derived from violet mudstone in the Puchanghe Formation below the Matoushan Formation.The deposit is of sedimentary (diagenetic) -later superimposed and remoulded origin. Ore formation might progressed through two stages: in the early stage source beds formed, and in the late stage orebodies deposited.