Study On Ore-forming Conditions And Mineral Resource Assessment Of Lead-Zinc-Silver-Gold Metallogenic Belt In Qingchenzi, Liaoning Province

Special attentions have been paid to gold and multimetal deposits formed in the Proterozoic era in recent years. Many important large to huge-size ore deposits of Fe Mn PbZn Cu Ni Au U P B Co as well as REE have been discovered in Proterozoic era. It's considered that the Proterozoic (especially Paleoproterozoic) is one of the most important mineralization periods in the world. The Proterozoic stratiform rocks are widely distributed in eastern Liaoning province and southern Jilin province located in the east part of northern margin of North China craton. A large amount of gold lead zinc copper cobalt as well as boron deposits have been discovered in this region. The most remarkable region is Qingchenzi metallogenic belt in the middle part of Liaoning-Jining rift. In this belt 12 medium to large-size lead-zinc deposits with 1500 thousand tons proven reserves have been discovered in round about 200 square kilometers. The well-known Qingchenzi lead-zinc deposit is one of them. In recent 10 years one large-size silver deposit and four medium to large-size gold deposits have been discovered in Qingchenzi neighbourhood with 209 tons gold and 1139 tons silver proven reserves and many preferred exploration areas. The study on ore-forming condition and mineral resources assessment of Qingchenzi lead-zinc-silver-gold metallogenic belt is of great significance to evaluate objectively the economic value and guide gold and multimetal resources assessment of this region. Since 2002 the author had been done a greate deal of research work in this metallogenic belt including Qingchenzi lead-zinc deposit Gaojiafuzi large-size silver deposit and several gold deposits. On the base of previous work the author chose the two crucial but disputing problems in this area--deposit genesis and ore-forming condition--as the study emphases of this paper took a series of comprehensive work on tectonic environment metallogenic formationmetamorphism characteristics and the geology geochemistry ore-forming conditiondeposit genesis of gold multimetal deposits built metallogenic model of this region conduct mineral resource assessment. After two and a half years work the author acquired such systematically recognitions to the Qingchenzi metallogenic belt as follows 1. The research region is located in Liaoning-Jining rift North China craton. The inland rift formed in the Paleoproterozoic era is between the Longgang block and Langlin block. During the period time of rift formation the sediment-lithogenesis and metamorphism-deformation in the Paleoproterozoic era magmation and tectonism in the Mesozoic provided plenty material and energy for the Qingchenzi Pb-Zn-Ag-Au multimetallic belt. 2.The Liaohe Group mainly Gaojiayu Suite Dashiqiao Suite and Gaixian Suite the most abundant lithologies occur in this region is composed of granulites marbles interbedding with schists. The protoliths of the group include carbon-rich mudstones siltstones impure carbonates and sillcalite which underwent greenschist to amphibolite facies metamorphism. It's showed that the distribution of lead zinc silver gold deposits are related to surrounding host rocks. Not only certain mineral deposit occurred in certain rock assembles but also different type deposits only occurs in different layer of the rock assemble. That's the important geological characteristics of the minerallgenic belt. 3. The formation and development of Paleoproterozoic syngenetic fault lied in the center part of the Liaoning-Jilin rift impact greatly on mineral deposits formation. A series of hydrothermal sedimentary rocks with rich silicon ferrior or carbonic tourmaline albites layout alone the fault show that the latter is the channels for hydrothermal eruption of Au PbZn Ag ore-forming fluid. The reducing environment caused by hydrothermal activity enriched hydrothermal catogene clay and carbonates with carbon as well as some sulfide such as pyrites. At the same time hydrothermal eruption brought much ore-forming elements such as Au Pb Zn Ag to the ocean basin from deep crust or underlying Archaean stratum and settled together with hydrothermal and other normal sediments which then formed source bed of metal deposits. The activity and intensity of the syn-genetic fault varied during forming process which resulted in the formation of different type and ore-forming elements assemblage deposits. 4. Gold is noticeable commodity in this metallogenic belt. The proven gold deserves in this region is more than 200 tons. Gold deposits occur mainly within marble low-grade granulite mica schists interlayered with sillcalite near the junction of upper Dashiqiao suite andGaixian suite. The main types of gold deposits in this region are as follows sillcation-hostedfracture zone-controlled sillcate marble-hosted and quartz fine-grained vein-related. The mineralizing component of gold deposit is very simple. Metal mass is only 4.15%. The ore minerals are composed of pyrite (about 2.66%) arsenopyrite (about 1.2%) and little amount of sphalerite galenite chalcopyrite tetrahedrite and magnetism. The gangue minerals include dolomites quartzs and minor sericites graphites. The texture of gold ores are idiomorphic granular texture allotriomorphic granular texture poikilitic texture crush texture metacrystal texture metasomatic-relict texture and so on. The main structure of gold ores is plicated and disseminated structure veinule disseminated veinule and ring structure also present in some deposits. The characteristics of field and geochemistry showed that the gold deposits in this region formed under syn-sedimentation together with metamorphism-deformation and hydrothermal alternation at late stage. 5. Silver is a prospective commodity in this belt with proven reserves of more than 1100 tons. Silver deposits mainly within marble low-grade granulite mica schists interlayered with sillcalite near the junction of upper Dashiqiao suite and Gaixian suite. The main types of silver deposits in this region include fracture zone-controlled sillcate marble-hosted and quartz fine-grained vein-related the first two of which are dominant. In large-size ores several mineralization types often operate together varied from sillcate marble-hosted type in upper orebeds to fracture zone-controlled type in deep orebeds. The texture of silver ores mainly include cryptocrystalline to fine-grained allotriomorphic granular idiomorphic to hypidiomorphic granular emulsion mosaic. The structure of silver ores is banded plicateddrusy brecciated ring disseminated and so on. Sedimentation and late hydrothermal alternation contribute to the formation of silver deposits. 6. 12 large to medium size lead-zinc deposits namely Zhenzigou Nanshan XixieshanBenshan Diannan deposit and so on have been discovered in the research region with the proven reserves of 1500 thousand tons. Much attention is put on the distinct concentration and typical field characteristics of lead-zinc deposits in this region. Most of the lead-zinc deposits occur in 5 resource beds in the Gaojiayu suite and the Dashiqiao suite with the character of zoning distribution in spatial along certain direction and with approximately same distance. Two types of ore body have been recognized. One type is stratiform and stratoid ore bodywhich occur in medium-deep part of ore-bearing metamorphic rocks. The other is irregular vein and pockety ore body which occur in medium-upper part of ore-bearing metamorphic rocks. The dominant ore minerals are sulfides. The minor one includes pyrites galenites sphaleritesarsenopyrites kroberites chalcopyrites and so on. The gangue minerals are calcites...