| The Motianling Granite in northern area of Guangxi is located at themargin of Yangtze craton and Cathaysia, in the southwest of JiangnanOrogen. Motianling Granite is attributable to uranium granites inSouthern China. The rock belongs to the S-type granites, its diageneticage is between760Ma-840Ma. According to the tectonic settingdiscrimination, the geochemical data shows that the rock mass is similarto volcanic arc granite (VAG) and Syn-collision granite. It is inferred thatrock formation from Ocean crust subduction continental crust, untilCollision orogenic role. There is a number of magmatism in the wholeprocess of Motianling granite formation.Motianling granite as one of the oldest uraniferous granites in China.There are two typical uranium deposits with differ metallogenetic epoch and ore-forming types, so it had aroused wildly concernd. A lot of reserchthe on Motianling granite had been done, but the uranium deposits in thegranite has a low degree of research, especially, there is nocontradistinction of the two typical deposits.There are two types of uranium deposits in granite:Pitchblende-Chlorite type and Pitchblende-siliceous veins type. Chlorite-type uranium was occur in the inner and outer contact zone of the graniteand wall rock, metallogenic epoch was Early Hercynian period,376deposit is typical deposit; siliceous veins-type uranium was occur ininternal silicified fault zone and the secondary fault zone, metallogenicepoch was from late Yanshanian to early Himalayan Epoch,374depositis typical deposit. In this paper carried out a detailed comparative study oftwo typical uranium deposits,and have made some recognizes as follows:1. There are several differences of two deposits showing up:1)Deposits wall rock has different structure. The ore of376deposit bodiesare produced in medium-grained biotite granite. But the ore of374deposit bodies are produced in coarse-grained biotite granite.2)Deposits have different structure characteristics. Geotectonic nature of the376deposit is mainly pressure and pressure-shear. Geotectonic Nature ofthe374deposit is mainly pressure-shear and tenso-shear.3) Alteration ofsurrounding sock are different types. Wall-rock alteration in376depositis based on the Caledonian regional metamorphism. Wall-rock alteration in374deposit is not only ralated to the characteristics of the Caledonianregional metamorphism, but it develop Wuzhishan linear silicifiedalteration transformation in the late Yanshanian.2. The similarities of the two deposits are showing up:1) Althoughthe mineralization of the two deposits is different, the main mineralcomposition of ore is same. The composition is asphalt uranium, andthere are secondary uranium mineral on the surface.2) The structure andtectonics of the ore are similar, the main ore structure include colloidalstructure and metasomatic residual structure, and the tectonic of the oreinclude mesh, stockwork, infection-like, breccia;3) The tectonic modelof the deposits is developed in the large fracture, and a lot of secondaryfault structure are developed around the regional fracture later.Mineralization had occurred after the regional tectonic framework. Thelarge fracture is the mineral migration pathways. Mineral are enriched inthe secondary faults. there is no strong tectonic movement after the endof the mineralization.Researching of geochemistry of376deposit and374deposit showthat: the geochemical characteristics of wall rock in deposits are similar,but geochemical characteristics of the ores in deposits are different.Through rare earth elements and the chronology research of the twodeposits, ore of376deposit is derived from the granite, ore of374depositis derived from the granite. but there is some signals from the deep earth. |
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