Metallogenic Epoch of Nonferrous Metallic and Silver Deposits in the Jiaodong Peninsula, China and its Geological Significance

As China＇s most important gold-producing district, the Jiaodong Peninsula also contains copper, lead-zinc, molybdenum （tungsten）, and other nonferrous metal ore deposits, but the space-time and genetic relationships with gold deposits remain uncertain. To investigate the temporal relationship between these nonferrous metal and gold ore deposits, We collected the samples from a number of nonferrous metallic and silver deposits and metallogenetic rock bodies in the eastern Jiaodong Peninsula for isotopic dating. The results show that the Re-Os isotopic model ages of the Lengjia molybdenum deposit in Rongcheng range from 114.5 ± 1.8 Ma to 112.6 ± 1.5 Ma, with an average age of 113.6 ± 1.6 Ma; the LA-ICP-MS ^206pb/^238U ages of 33 zircons in the sericitization porphyritic monzogranite that hosts the Tongjiazhuang silver deposit in Rongcheng range between 122 Ma and 109 Ma, with a weighted mean age of 116.04 ± 0.95 Ma; the LA-ICP-MS ^206pb/^238U ages of 31 zircons in the copper metallogenic pyroxene monzodiorite that hosts the Kuangbei copper deposit in Rongcheng range from 126 Ma to 106 Ma, with a weighted mean age of 116.6 ± 1.7 Ma; and the LA-ICP-MS ^206pb/^238U ages of 19 zircons in the pyroxene monzodiorite surrounding the Dadengge gold and multimetal deposit in Weihai range from 113 Ma to 110 Ma, with a weighted mean age of 111.7 ± 0.6 Ma. All these results indicate that the metallogenic ages of the silver and nonferrous metallic deposits in the Jiaodong Peninsula are in a limited range from 118 Ma to 111 Ma. Previous studies have demonstrated that the isotopic ages of gold deposits in the Jiaodong Peninsula range from 123 Ma to 110 Ma, while Weideshanian magmatism occurred between 126 Ma to 108 Ma. Both these ranges are grossly consistent with the metallogenic ages of silver and nonferrous metallic deposits in this study, suggesting that the large-scale mineralization occurred in the Early Cretaceous when magmatic activities were strong. This epoch may be linked to the lithosphere thinning and the thermo-upwelling extension in eastern China at that time. In addition, field investigation also shows that gold and nonferrous metallic deposits are distributed nearby the Weideshanian granite, with the nonferrous metallic deposits lying within or surrounding the granite pluton and the gold deposits outside the granite pluton. We propose the following mineralization scenario： In the Early Cretaceous, an intensive lithospheric extension induced partial melting and degassing of the metasomatized lithospheric mantle, which resulted in the formation of mantle-derived fluids enriched in metal elements. During the rapid process of magma ascent and intrusion, crust-derived fluids were activated by the magmatic thermal dome and served to further extract ore-forming materials from the crust. These fluids may have mixed with the mantle-derived fluid to form a crust-mantle mixing-type ore-forming fluid. The high-temperature conditions in the center or in contact with the granitic magmatic thermal dome would have been favorable for the formation of porphyry-type, skarn-type, and hydrothermal-vein-type ores, thus forming a series of Mo（W）, Cu, and Pb-Zn deposits in the mid-eastern Jiaodong Peninsula. In contrast, the medium- to low-temperature conditions in the periphery of the magmatic thermal dome would have favored the deposition of gold （silver） ores under the appropriate physiochemical and structural conditions. The metaliogenic epoch of the molybdenum, copper, and silver deposits, and their spatio-temporal and genetic relations to the gold deposits, as demonstrated in this study, not only provide important insights to the study of regional metallogeny, our understanding of the metallogenesis of the Jiaodong type gold deposit, and the geodynamic background of the large-scale mineralization in the Jiaodong Peninsula, but also have practical value in guiding the mineral exploration.

Structural deformation, metallogenic epoch and genetic mechanism of the Woxi Au-Sb-W deposit, Western Hunan Province, South China

The remobilization,migration,precipitation,and enrichment of ore-forming elements are closely related to structures.Therefore,detailed regional and ore-field structural analyses are critical for determining the genesis of a mineral deposit.The Jiangnan Orogenic Belt(JOB)is an important gold polymetallic metallogenic belt in South China,which is characterized by multiple periods of gold mineralization in the Paleozoic and Mesozoic.However,the genesis of these gold polymetallic deposits is still not well understood due to a lack of systematic research on the regional geology,ore-controlling structures and metallogenic mechanism.In this study,a detailed structural survey at the surface and in the subsurface tunnels was conducted on the Woxi Au-Sb-W deposit,the genesis of which is relatively controversial among the gold polymetallic deposits in the JOB due to poor structural constraints.In addition,a wolframite U-Pb dating was carried out to further constrain the relationship between structures and mineralization.Based on the results of these studies,together with those from previous studies,it is proposed that the Woxi deposit and surrounding areas likely underwent six periods of regional deformation,which are constrained in time and geodynamic setting.Furthermore,we present a systematic discussion on the roles of ore-controlling structures in the transportation,distribution,and deposition of ore-forming elements and localization of orebodies.According to the wolframite dating results,structural analyses,and previous data,we propose that the Woxi Au-Sb-W deposit was formed in two stages during the Yanshanian:a W(wolframite)-Au mineralization stage at ca.140 Ma and an Au-Sb-W(scheelite)mineralization stage at<130 Ma.These mineralizing events are interpreted to have a tight relationship with tectonic reactivation,and the ore-forming fluids were derived from deep sources,including those of magmatic or metamorphic origins.The Woxi deposit can therefore be classified as an“intracontinental reactivation-type”,and the mineralization is related to lithospheric extension caused by plate retreat,retention,and delamination following the cessation of westward subduction of the Paleo-Pacific Plate beneath the East Asian continent.

Hydrothermal Alteration Mapping in Northern Khur, Iran, Using ASTER Image Processing: a New Insight to the Type of Copper Mineralization

Eastern Iran has great potential for the discovery of different types of mineralization. The study area encompasses Tertiary magmatism in the northern Lut block located in northern Khur, South Khorasan, eastern Iran and is mostly covered by volcanic rocks, which are intruded by porphyritic subvolcanic intrusions in some places. Application of the spectral angle mapper （SAM） technique to Advanced Spaceborne Thermal Emission and Reflection Radiometer （ASTER） images detected sericitic, argillic, and propylitic alterations, silicification, and secondary iron oxides. The alteration is linear and associated within vein-type mineralization. Twelve prospective areas are selected for detailed exploration and based on our processing results, in addition to NW-SE faults, which are associated with Cu mineralization indications, NE-SW faults are also shown to be important. Based on the presence of subvolcanic rocks and numerous Cu ± Pb-Zn vein-type mineralizations, extensive alteration, high anomaly of Cu and Zn （up to 100 ppm）, the age （43.6 to 31.4 Ma） and the initial $78r/S6Sr ratio （0.7047 to 0.7065） of the igneous rocks, and the metallogenic epoch of the Lut block （middle Eocene-lower Oligocene） for the formation of porphyry Cu and epithermal deposits, the studied area shows great potential for porphyry copper deposits.

Intrusion-related Gold Deposits in Egypt

Intrusion-related gold deposits(IRGDs)occur in the Eastern Desert(ED)of Egypt within magmatic districts that are exploited for tungsten and tin mineralization.IRGDs and intrusion-related rare metal deposits(IRRMDs)are almost invariably linked with the late to post collisional Younger Granites(YGs)that have three successive phases(Ⅰ,ⅡandⅢ).At~635–630 Ma,the ED underwent a transition in deformation style from compressional to extensional and a switch from subduction with crustal thickening to delamination with crustal thinning.This transition was concurrent with the emplacement of a short magmatic pulse(~635–630 Ma)that represents a transition between orogenic gold deposits and IRGDs.K-rich calc alkaline granites(phaseⅠandⅡof the YGs)hosting IRGDs like the Hangalia deposit were emplaced during the time span 630–610 Ma.Alkaline magmatism began at 610 Ma,coexisting with the K-rich calc-alkaline magmatism over the 610–590 Ma time span,where the Fawakhir(598±3 Ma)and Um Had(596±2 Ma)granites that host the IRGDs were emplaced.In time,the alkaline magmatism became more alkaline giving rise to phaseⅢof the YGs that hosts IRRMDs.A distinct metallogenic epoch comprising both IRGDs and IRRMDs,was undergoing extreme growth at~600 Ma.

Main deposit styles and associated tectonics of the West Junggar region,NW China

The West Junggar region, located in the loci of the Central Asian Orogenic Belt, is a highly endowed metallogenic province with 〉100 tonnes Au, 〉0.7 Mt Cu, 〉0.3 Mt Mo, and 〉2.3 Mt chromite as well as significant amounts of Be and U. The West Junggar region has three metallogenic belts distributed systematically from north to south： （1） late Paleozoic Saur Au-Cu belt; （2） early Paleozoic Xiemisitai- Sharburt Be-U-Cu-Zn belt; （3） late Paleozoic Barluk-Kelamay Au-Cu-Mo-Cr belt. These belts host a number of deposits belonging to at least eight economically important styles, including epithermal Au, granite-related Be-U, volcanogenic massive sulfide （VMS） Cu-Zn, podiform chromite, porphyry Cu, hydrothermal quartz vein Au, porphyry-greisen Mo（-W）, and orogenic Au. These deposit styles are associated with the tectonics prevalent during their formation. Five tectonic-mineralized epochs can be recognized： （1） Ordovician subduction-related VMS Cu-Zn deposit; （2） Devonian ophiolite-related podiform chromite deposit; （3） early Carboniferous subductionrelated epithermal Au and porphyry Cu deposits; （4） late Carboniferous subduction-related granite-related Be-U, porphyry Cu, and hydrothermal quartz vein Au deposits; and （5） late Carboniferous to early Permian subduction-related por- phyry-greisen Mo（-W） and orogenic Au deposits.