Redetermination of the Depositional Age of the Haerdaban Group in the Northern Margin of the Yili Block,Western Tianshan,NW China:Implications for Regional Tectonics and Pb-Zn Mineralization

The Yili Block in the Western Tianshan orogen is a key area for understanding the early crustal formation and evolution of the Central Asian orogenic belt,due to the widely-distributed Precambrian rocks.Also,it hosts a lot of medium–to large-scale sedimentary exhalative(SEDEX)Pb-Zn deposits that mainly occur in Proterozoic metamorphosed clasticcarbonate rocks.In this study,LA-ICP-MS U-Pb analyses were carried out on detrital zircons in siltstones of the Precambrian Haerdaban Group in the Haerdaban Pb-Zn deposit and magmatic zircons in the diorite dyke that cuts through the strata and orebodies.The maximum depositional age of the siltstones was determined to be about 604 Ma,the diorite having formed at approximately 500 Ma.As such,the Haerdaban Group was most likely formed in the Neoproterozoic Sinian,rather than the previously considered Mesoproterozoic Changchengian.Detrital materials of the Haerdaban Group were mostly derived from the Nanhua–Sinian mafic dykes and granitic rocks around Lake Sayram at the northern margin of the Yili Block.It is proposed that the Yili Block,together with the Kazakhstan and Central Tianshan blocks and the Tarim Craton,might all pertain to the same Rodinia supercontinent,which has great potential for targeting large to super-large SEDEX Pb-Zn deposits.

Research Progress of the Mineralization of Carbonate-Hosted Pb-Zn Deposits in the Sichuan-Yunnan-Guizhou Pb-Zn Metallogenic Province, Southwest China

The Sichuan-Yunnan-Guizhou （SYG） Pb-Zn metallogenic province in the western Yangtze Block, is a key component of the low-temperature metallogenic domain in South China. In this area, more than 400 Pb-Zn deposits have been discovered, and the total proven reserves are up to 260 million tons with lead and zinc grade reaching 10%, even up to 30%.

Preliminary Study of the Characteristics and Genesis of Arsenate Minerals in the Oxidized Zone of the Debao Skarn-Type Cu-Sn Ore Deposit in Guangxi

Through the study of the oxidized zone of the Debao skarn-type Cu-Sn deposit in Guangxi, the authorshave found 14 arsenate minerals, most of which are for the first time reported in China. They are mainly Cuarsenate minerals with subordinate Cu-Pb arsenate minerals and minor Fe-Pb-Ba varieties. Based on their paragenesis these minerals may be divided into the following series: (1) the clinoclasite-olivenite-cornwallite- cornubite- debaoite- copper silicarsenate association, (2) the scorodite- carminite- beudan-tite-bayldonite- duftite association, and (3) the scorodite-Ba-bearing pharmacosiderite- dussertite association. Arsenate minerals are formed generally in the oxidized zone of the sulfide-type deposits which lie in thewarm, humid and rainy torrid-subtropical zone with pH=6-8 and contain large amounts of arsenopyrite andcarbonate rocks.

Cenozoic Mineralization in China,as a Key to Past Mineralization and a Clue to Future Prospecting

Many Cenozoic metal deposits have been found during the past decade. Among them, the Fuwan Ag deposit in Guangdong is the largest Ag deposit in China. Besides, the largest Cu deposit of China in Yulong, Tibet, the largest Pb-Zn deposit of China in Jinding, Yunnan, and the largest Au deposit of China in Jinguashi, Taiwan, were also formed in the Cenozoic. Why so many important “present” deposits formed during such a short period of geological history is the key problem. The major reason is that different tectonic settings control different kinds of magmatic activity and mineralization at the same time. In southwestern China, porphyry-type Cu deposits such as Yulong were formed during the early stage of the Himalayan orogeny, sediment-hosted Pb-Zn deposits such as Jinding were formed within intermontane basins related to deep faults, and carbonatite-related deposits such as the Maoniuping REE deposit and alkalic magmatic rock-related deposits such as the Beiya Au deposit originated from the mantle source. In southeastern China, the Fuwan Ag deposit was related to continental rifting which was triggered by the mantle plume. In Taiwan, the Jinguashi Au deposit was formed during the subduction process of an oceanic plate beneath a continental plate. Besides, the features such as the diversification, inheritance, large size, deep source of metals and fluids of the Cenozoic (Present or Recent) mineralization can be used as a key to the search for past deposits.

Constraints on the Genesis of the Qixiashan Pb-Zn Deposit, Nanjing: Evidence from Sulfide Trace Element Geochemistry

The large-scale Qixiashan Pb-Zn Deposit in the eastern Middle-Lower Yangtze metallogenic belt is hosted in carbonate rocks.Based on a detailed mineral paragenesis study,in-situ LA-ICP-MS(laser ablation inductively coupled plasma mass spectrometer)trace element geochemistry data for pyrite and sphalerite from different stages in the Qixiashan Deposit are reported,the Pb-Zn mineralization processes are reconstructed,and a genetic model is constructed.Four paragenetic stages of Pb-Zn ore deposition are identified:the biogenic pyrite mineralization stage(Stage 1),the early stage of hydrothermal Pb-Zn mineralization(Stage 2),the late stage of hydrothermal Pb-Zn mineralization(Stage 3),and the carbonate stage(Stage 4).Stages 2 and 3 are the main ore stages.The trace element characteristics of the sulfide in stages 2 and 3,such as the higher Co/Ni and lower trace element contents of the pyrite and the Fe,Mn,and Ge contents of the sphalerite,indicate that they were generated by magmatic-hydrothermal processes.Furthermore,the lower Cu,Ag,Sb,and Pb contents of the pyrite and sphalerite of Stage 3 compared to Stage 2 suggest an increase in magmatic-hydrothermal activity from Stage 2 to Stage 3.The hydrothermal fluids leached trace elements(e.g.,Cu,Ag,Sb,and Pb)from the previously deposited primary pyrite and sphalerite,which were precipitated in the later hydrothermal stage Cu,Au,Ag,Sb,and Pb bearing minerals and secondary pyrite and sphalerite with lower trace element contents(e.g.,Cu,Au,Ag,Sb,and Pb).Compared with the pyrite from stages 2 and 3,the Stage 1 pyrite has relatively higher trace elements contents(Sb,Cu,Zn,Au,Ag,Pb,As,and Ni).However,their lower Co/Ni ratio suggests a syngenetic sedimentary origin.Based on the petrographic features and trace element data,a multi-stage mineralization model is proposed.The Stage 1 biogenic pyrite formed stratiform pyrite layers,which provided reducing conditions and a base for the subsequent Pb-Zn mineralization.During Stage 2,subsequent hydrothermal fluid interacted with the stratiform pyrite layers,which resulted in sulfide precipitation and the formation of stratiform Pb-Zn orebodies.In Stage 3,the hydrothermal fluid replaced the limestone along the fractures,which triggered the formation of Pb-Zn vein orebodies.