Geological Characteristics And Genesis Discussion Of Chambishi Copper Deposits In Copperbelt Province,Zambia

Based on the Exploration Technology Methods Integration of Zambian Copper Polymetallic Ore and Target Selection and Prospecting Research on Copper-Molybdenum Squat in Southeast Chambishi Copper Mining Area undertaken by China Nonferrous Metals(Guilin) Geology and Mining Co., Ltd., this paper studied the geologic features of the sedimentary pattern copper mine and hydrothermal copper molybdenum ore by the collection of the existing research and systematic field and laboratory work. The mineral deposit genesis is discussed by the comparative analysis of lithogeochemistry, mineral fluid inclusions, sulfur isotope, rare earth elements, and Re-Os isotopic dating, etc. Main results and understandings achieved are as follows:(1) Located in the north margin of Chambishi-Nkana Mineragenetic Basin, the Chambishi copper mine is under the impact of Kafue anticline and the terrine nous shallow marine sediment environment. The ore body occurs in horizontal bed in the ore rock of lower Roan Formation with long extension, large thickness and high grade, presenting the features of a super-large sedimentary pattern copper ore. The hypabyssal vein copper-molybdenum mineralization at the bottom of main ore body has a certain scale, which is distinctive from sandy shale sedimentary copper ore regarding mineralization conditions,ore-controlling factors, wall rock alteration, and concentration regularity.Thus the notion that there is hypomagma hypabyssal copper-molybdenum mineralization is proposed.(2) The element association of hydrothermal veins copper-molybdenum mineralized rock is Cu-Co-Mo-Bi with hypothermal mineral association, indicating that material source of Mo element may be related to the enrichment of ore-bearing hydrothermal activity. The element association of sedimentary deposit rock is Cu-Co with low Mo abundance, showing a terrestrial ore-forming material source.(3) The homogenization temperature of fluid inclusion is concentrated in 100~350 ?,with the peak being 200~250 ?. The late superimposed vein copper-molybdenum mineralization temperature is mainly mesotherm, which is a peak of hydrothermal activity,indicating that the bottom of mother-lodes of the Chambishi Copper Mines is subjected to the post-mineralization superposition of the same metallogenic hydrothermal source. The composition of fluid inclusions shows that the ore-forming fluid should be Na+-Ca2+-Mg+-K+-Cl--CO32-system, which belongs to Cl-Na-Ca aqueous solution. The salinity is low, ranging between 10% and 20%.(5) Molybdenite Re-Os isotopic dating manifests that the mineralization time of molybdenite is 503±5Ma~509.3±5.7Ma and the isochron age is 509.3±5.7Ma, which should falls in the late Cambrian. Its formation age is obviously later than that of the sedimentary pattern copper mine in the Lower Roan layer(850-760Ma)but it is consistent with late orogenic movement time(600-480Ma) of Lufilian-thermo-event.(6) Chambishi Copper Mines have two mineralization types, namely sedimentary copper mine and magmatic hydrothermal copper molybdenum mine. The bedded deposit in early Lower Roan formation belongs to sedimentary type and the late magmatic hydrothermal copper molybdenum mine has the metallogenic characteristics of deep-seated ore-bearing hydrothermal solution, which has significant superimposed enrichment on sedimentary copper mine. The notion that deep part has magmatic hydrothermal copper-molybdenum mineralization and the discovery of such type of copper-molybdenum provides a new prospecting direction for this mining area.