| 辽吉海积寒武纪石膏矿床 |
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| 引用本文：.1985.Cambrian marine sedimentary gypsum deposits in Liaoning and Jilin provinces[J].Mineral Deposits,4(3):85~94 |
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| Cambrian marine sedimentary gypsum deposits in Liaoning and Jilin provinces |
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| Abstract:The discovery of Early Cambrian marine sedimentary gypsum(anhydrite) deposits is of great economic significance. The minerogenetic region belongs geotectonically to the eastern extension of Tianshan-Yinshan latitudinal tectonic belt, or to the Taizihe-tIunjiang synclinorium area of Eastern Liaoning anteclise of Sino-Korean paraplatform, Cambrian strata are well-developed with the total thickness of about one thousand maters. The gypsum deposits found in Liaoning occur in Lower Cambrian Mantou Formation and Jianchang Formation, while those discovered in Jilin are present only in Mantou Formation. The gypsum(anhydrite) bearing sedimentary sequence can reach 150 m in total thickness, and contains several rhythms or cyclothems made up of limestone, dolomite, gypsum(anhydrite)rock, red dolomitic mudstone and argillaceous dolomite, belonging therefore to “carbonate-evaporite-red bed formation” and “carbonate-gypsum(anhydrite)formation”. According to such phase indicators as rock type, texture and structure, mineral association and biological characteristics, the paleogeo graphical model for Early Cambrian gypsum(anhydrite)deposits of this region is the combination of intertidal flat, supratidal flat and lagoon subphases. The Early Cambrian gypsum(anhydrite)deposits have the following minerogenetic regularities and ore—prospecting indicators: 1．Ore-forming basins all occur in downwarping areas within the paraplat form; sedimentation center or concentration of gypsum(anhydrite)are strictly conditioned by tectonic unit of grade IV; the downwarping areas are characterized by continuous uplifting and subsidence, which are most favorable for mineralization when the surrounding areas have abundant ore-forming materials to supply them. 2．Economic gypsum(anhydrite)deposits occur in Mantou Formation and Jianchang Formation. In the former formation, the major ore bed is present in the red bed on the top, while in the latter formation, ore bed occurs as intercalation in carbonate rock. Gypsum(anhydrite)beds are unexceptionally found at the relatively upper part of the regression rhythm. Vertically, the deposits are characterized by apparent eyclothem, some basins even show zonal distribution in plane. 3．The phase indication minerals of ore-bearing part are mainly gypsum,Anhydrite, celestite and fine-grained dolomite; phase indicators are pseudomorphic crystal of salt, red bed, lamination, ripple mark, rain-print, drying crack, bird’s eye texture and so on. 4．The deposits have obvious zonation. From the surface downward, 1eached horizon→gypsum zone→gypsum-anhydrite zone→anhydrite zone can be distinguished. Geochemical indicators for gypsum bed at surface are: Ca/Mg ratios usually approximating to 4-6; Sr/Ba and B/Cd ratios being slightly higher than their background Values. 5．Generally speaking, the following conditions are favorable for ore presserration: simple structure at late ore-forming stage; imperfect development of fractures in mining districts; relatively simple hydrogeological conditions; weak connection between ore bed at depth and surface or underground water; existence of good water-resisting layers both above and beneath the ore bed. |
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