The Detailed Structure Comparison Of Ore Bearing Horizon And Ore Belt From Gacun-Yure Ore District And Its Prospecting Significance

Located at Baiyu county of Sichuan province, the Gacun silver-bearing polymetallic deposit, which has a “Trinity type” rock assemblages consisting of volcanic series as host rocks, sulfide ore bodies and exhalite as well as a “double-layered structure” with tubular or funnel stockwork ores at the lower part(the western zone) and laminated massive ores at the upper part(the eastern zone), is one of the most typical VMS deposits in China.Though deposited to the south of Gacun deposit, it is still dispute whether the Youre area and Gacun deposit belong to the same ore-bearing layer and the Youre area exist concealed silver-copper-lead-zinc ore bodies that and similar with the eastern ore belt of Gacun represented by “black ore”-barite association.Based on detailed field investigation of Gacun-Youre ore district,combined with the microscopic observation and map data,we preliminarily discussed its ore bearing horizon and ore belt detailed structure.(1)Detailed strata correlation studies showed that the ore-bearing layers of the Youre area and Gacun deposit are both characterized by continuous and steady geopetal mark layer and vertically lithologic variation from media-acid rock associations at the lower part to acid rock associations at the upper part. From bottom to the top of the ore-bearing layer, the rock association changed from rhyodacite breccia at the bottom,through rhyodacite breccia lava and volcaniclastic rock at the lower part and rhyolitic lava volcaniclastic rock at the upper part, to the calcareous carbonaceous slate and overlying andesites at the top. Given the evidence above, we inferred that the Gacun-Youre ore district are within the same ore bearing layer and that the Youre ore district is part of Gacun ore body expands to the south.(2)The detailed structure comparison of ore belt from Gacun-Youre ore district suggests that the northern prospecting line 19-31 of Youre mining area, which consists of volcanic units including massive silicide rhyolitic volcanics, striped or ribbon rhyolitic tuff, phyllitic sercite tuff characterized by heavy silicification and vein-network structure, correlates well with that of the Gacun deposit. On the other hand, unlike the eastern zone of Gacun deposit, which characterized by barite-rich with predominantly “black ore” forming the high grade silver-copper-lead-zinc ore bodies, the southern line 39-55 of the Youre mining area is just composed of exhalite-volcanic units including the massive “yellow ore” and rhyolitic clastic rock but lacking exhalite such as barite and siliceous rocks, forming the lower grade lead-zinc ore bodies. Meanwhile, the occurrence of rhyolitic volcanics and vein-stockwork ore bodies with a total thickness of 70-130 m overlying the upper part of massive ore bodies in Youre mining area indicates that the Youre ore belt could correlate with the western zone of the Gacun deposit overall. It could represent the hot water supply pipe facies of the hydrothermal exhalative metallogenic system, wherein the massive(yellow ore) ore bodies characterized by a “double-layer” structure assembling another independent “micro” VMS deposit during the early stage of the hydrothermal metallogenic system.(3)Therefore, concealed silver-copper-lead-zinc ore bodies may exist eastern to the known ore body of the Youre mining area, similar type with that of the eastern Gacun ore belt represented by “black ore”-barite associations. Finding such type of ore body could be the key to the breakthrough of further prospecting in Youre mining area.