Geological Characteristics, Mineralization Regularities And Origin Of Zhulazaga Gold Deposit In Inner Mongolia

The Zhulazaga deposit is a super-large gold deposit discovered for the first time in the Middle-Upper Proterozoic Suberathem in the western section of the north edge of North China platform. A comprehensive study has been carried out on the regional geology, mining area geology and ore-deposit geology combined with isotope geology, metallogenic conditions, mineralization regularities and genetic types of the ore deposit in this paper. The main achievements obtained in this paper are as follows:1. Some of new recognitions were obtained on such aspects as strata sequence, rock type, metamorphism, hydrothermal alteration and the sedimentary environment by the study on many profiles in this area, with discovery of volcanic rocks for the first time in ore-bearing strata and ore bodies. Through further petrology and isotope chronology studies on granite-porphyry distributed in mining area, we thought that the granite-porphyry played a very important role in the formation of the Zhulazaga gold deposit. The lithologies of intrusive rocks were re-determined, for example, the rock previously named as diorite in southern area was renamed as gabbro, and the dike rock distributed along NNW as spessartite which was related to formation of the Zhulazaga gold deposit to some extent.2. It is discovered by research on the ore deposit, ore bodies and ores that the Zhulazaga deposit is formed in two stages with quite different geological structure environment and large geological time gap. The mineralization of early stage in the form of exhaust-sedimant formed by seafloor volcanic activities provides a solid foundation for the mineralization of later stage. In the late stage of mineralization occurred in the Hercynian period, a widespread strong modification of ores or mineralized rocks of early stage caused by intrusion of parental magma of granite-porphyry leads to further enrichment of gold element and eventual formation of the gold deposit. 6 34S of sulphide in the ore vareis from 1.1 - 7.1 ‰ with an average of 2 ‰ , showing characteristics of hydrothermal mineralization related to deep source magma. It was also indicated by the studies on a large number of Pb isotope that Pb in ores of the deposit chiefly came from volcanic rocks in the strata and later intrusions with derivation of a little Pb from the normal deposit stratum. The analyses of oxygen and hydrogen isotope indicate that the hydrothermal fluid is dominated by magmatic water with input of a lot of meteoric and underground water in the later stage.3. The hydrothermal activities which were complicated and acted a positive effect in the formation of the Zhulazaga gold deposit resulted in hydrothermal alterations of multiepisode, including pyroxeneization, actinolitization, epidotization, ice-feldsparization, silicification, chloritization and carbonatization etc. The research on inclusions in quartz of the ore indicates that the hydrothermal fluid varying greatly in temperature with an average of 286℃ shows characteristics of high temperature. Moreover, the hydrothermal fluid is also very high in salinity with an average of NaCl = 21.66 Wt% and relatively lower in pressure with an average of 54× 105Pa. There was a tendency of salinity decreasing with decreasing of pressure.. 4. The ore type is multitudinous in Zhulazaga gold deposit, including exhaust-sediment type, alteration volcanic rock type, alteration metamorphic sandstone type, metasomatic rock type and sulfide quartz vein type, of which the strongest one contributed to deposit was the alteration metamorphic sandstone type, and the secondary one is alteration volcanic rock and metasomatic rock type. It was found initially that the carrier of gold was the independent gold mine, predominantly the nature gold, sulphide was the chief one among other minerals.5. It is noteworthy for prospecting in surrounding area and vicinity of Zhulazaga gold deposit as follows: the first lithologic segment of Maodao formation is an important ore-bearing stratum, trace acco...