Study On The Metallogenesis In The Geological Surface Of Pb-Zn-Sn Polymetallic Deposits And Their Prospecting Prognosis In The Middle Guangxi Depression

Geological surfaces, the contacting parts between two or more geological bodies (including geological fluids), are the transition zones that change suddenly. The geological bodies (including geological fluids) on both sides of the surface present difference in lithology, minerals, chemical composition, structure, texture, and other geophysical and geochemical characteristics. The metallogenesis in the geological surface is in fact the main type and the important pattern of the structure controlling ore-forming. The metallogeneses at the surface involve not only simply the space of the metallogeneses, but also the physical, chemical and biochemical processes. The key problems of metallogeneses in geological surfaces are the formation, the evolution, and the movement of the structure surface and ore-forming fluid, and also including the coupled relation between each other.The middle Guangxi depression is located neighbouring to Northern Guangxi Uplift in the north, Pingxiang-Dali deep fault in the south, Dayaoshan Uplift in the southeast. It is separated by Longsheng-Yongfu-Dongxiang deep fault in the northeast from Northeastern Guangxi Depression, and by Nandan-Hechi-Kunlun deep fault from Youjiang tough in the west. The middle Guangxi depression, one part of the Nanhua rift in the mobile belt between Yangtze and Cathaysian old land as a rift-trough type basin is a great sedimentary sag of late Paleozoic, around which many kinds of geological surfaces in different orders had developed. After Caledonian Movement, Nanhua rift closed and withered away, and Cathasian block and Yangtze block joined together to form the ancient Southern China Continent. Central Guangxi-Northeastern Guangxi and Western Guangxi, the main places in which the opening-closing movement took place several times between Yangtze and Cathaysian blocks, are the weak zones where regional tectonic movements were rather strong. During the period of D-T2, and the course of the formation and extension of South China continent, Central Guangxi-Northeastern Guangxi kept on sinking, which made the formation of the large scale middle Guangxi depression and northeastern Guangxi depression having the characters of continent marginal basins.The periphery of the middle Guangxi depression is abundant in lead-zinc-tin-polymetallic resources. More than10super large scale or big-and-middle-sized deposits, and several hundreds of small deposits had been found, such as Nandan-Dachang super large scal tin-polymetallicdeposit, Beishan and Bailong large scale Zinc-Lead deposits, Damingshan larg scale tungsten deposit, Longtoushan, Fuliuling and Liujiuding middle scale gold deposits Liangjiang middle scale copper deposit, Siding middle scale Zinc-Lead deposits, and etc. A. these deposits occurred in space, such as (1) the borders between sedimentary basin and th uplift;(2) the surfaces of angle unconformities and the strata in the above and the below;(3) th circumstance of intermediate-acid intrusive bodies;(4) the intersection belts of several group o faults. The formation of all these spaces was evidently controlled by the geological surface which present in the surrounding of the Depression, representing the characteristics that th geological surface determined the formation of diagenesis and mineralization.The geological surfaces which occurred in the surrounding of the middle Guangx depression can be classified into three orders:Yangtze ancient continent marginal structure; dee(?) large faults, the unconformities and the large contact zone of rock bodies betweei Devonian-Cambrian strata; middle-small scale structure systems, which were the first, th(?) second and the third order mineralization controlling surfaces, respectively. According to th(?) geological processes of the formation, geological surfaces can be divided into:the surface: formed by sedimentation (including the unconformities, boundary surfaces of strata sequenc(?) and plurilocellate biolithite limes and dolostone); the surfaces formed by magmatism (including contact zones of rock masses and volcanic apparatus); the surfaces formed by tectonizatior (including ancient continent margins, deep faults, fissure system of secondary faults/diaclasses fold collapse part, slippages/shuttered zone between layers, and etc). In the present dissertation the mineralization controlling of geological surfaces was discussed in the orders respectively.Based on the mineralization and ore-controlling of the geological surfaces, the lead-zinc-tin(?) polymetallic deposits around the middle Guangxi depression were grouped into three types lead-zinc-polymetallic deposits controlled by the geological surface of the sedimentation type gold-copper-polymetallic deposits controlled by the geological surface of the magmatic type tin-polymetallic deposits controlled by the geological surface of the complex type. The minerogenetic condition, geological and geochemical characteristics, and the metallogenesis o(?) all the deposits were discussed in the present dissertation.The lead-zinc-polymetallic deposits relating to the geological surface of sedimentation type are the deposits which formeded in the sedimentary rock near the sedimentary unconformities ir the margin of the Central Guangxi basin. These deposits were related to the hot brine in the basir and developed by the alteration of many kinds of non-magmatic origin fluids of the basin, belonging to MVT lead-zinc deposits. The gold-copper-polymetallic deposits relating to the geological surface of magmatic type formed in the contact zones and the surrounding area of the medium-acidic magmatite occurred near the uplift side in the transition zone between the margin of the Central Guangxi basin and the uplift. These were related to the acidic and medium-acidic middle-small size magmatite bodies, and formed by the metasomatism and the filling of magma-origin hydrotherm, belonging to the magmatic hydrothermal or volcanic-subvolanic hydrothermal type deposits. The tin-ploymetallic deposits, concerning the geological surface of the complex type, occurred in the contact zones and the surrounding area of the concealed or half concealed medium-acidic magmatite in the deep faults of the Central Guangxi basin margin. These deposits were mainly developed by the synsedimentation in Devonian and alteration and enrichment of medium-acidic magmatite in Yanshanian, falling into the type of tin-ploymetallic deposits with the recombination metallogenesis of the magmatic hydrothermal and hot brine in the basin.Based on the theory of the mineralization and ore-controlling of the geological surfaces, the metallogenic and the prospecting models were established for the lead-zinc-polymetallic deposits relating to sedimentary geological surface, the gold-copper-polymetallic deposits concerning magmatic geological surface and the tin-polymetallic deposits connecting with the complex geological surface, respectively. On the basis of the results of the investigation and evaluation of land and resources in recent years, five prospecting areas with large or super-large scale resource potential were preliminary delineated by the method of similar analogy. They are Panlong-Silv lead-zinc deposit in Wuxuan county, Liuzhang tungsten-copper-molybdenum deposit in Binyang county, Beixiang tin-ploymetallic deposit in Hechi city, Luofu lead-zinc-polymetallic deposits in Nandan county, and Longshan silver-lead-polymetallic deposits in the town of Guigang.