Mineralization Of Sediment-hosted Lead-Zinc Deposits In The Middle-East Segment Of The Neo-Tethys Tectonic Domain

The Tethys metallogenic domain is one of the three major metallogenic domains in the world(Circum Pacific,Tethys,and Paleo-Asia).This domain has a large number of world-class sediment-hosted Pb-Zn deposits,such as Mehdiabad(21 Mt of Pb+Zn metal reserves),Huoshaoyun(19 Mt of Pb+Zn metal reserves),Jinding(15 Mt of Pb+Zn metal reserves),and Duocaima(8 Mt of Pb+Zn metal reserves)deposit.At present,the genetic type of these deposits is highly controversial.Two different opinions were proposed,Sedimentary Exhalative(SEDEX)Pb-Zn deposit and the Mississippi Valley Type(MVT)Pb-Zn deposit which hampers the understanding of ore-forming processes of Pb-Zn deposits and further prospecting in this metallogenic domain.Although numerous achievements and advances in geology and geochemistry have been made for these deposits,there are still some scientific issues that have attracted much attention,such as how did the ore-forming fluid and metallic materials of MVT-type deposits rapidly precipitate in the fold-thrust system of the Tethys domain?what are the metallogenic age and metallic enrichment mechanisms of the SEDEX-type Pb-Zn deposit in the Tethys domain?Therefore,the research on these issues will be conductive to understanding the genesis of sediment-hosted Pb-Zn deposits in the Neo-Tethys metallogenic domain.Combining previous research results and current exploration works,the Duocaima,Quemocuo,and Duddar deposits in the Middle East segment of the Tethys were selected to trace the ore formation processes of Pb-Zn mineralization.The main aims of this work are to describe the fine metallogenic process of different genetic types of Pb-Zn deposits(MVT and SEDEX)and to perfect the Pb-Zn metallogenic model.In addition,by comparing the metallogenic characteristics of these typical deposits,aiming to reveal the Pb-Zn mineralization under different tectonic environments and to summarize the spatial and temporal distribution of Pb-Zn deposits,and finally to enlighten the Tethyan tectonic evolution and prospecting.The main conclusions and findings of this paper as below:(1)Enriching and perfecting the Pb-Zn metallogenic theory in the Tethys domain.It is suggested that the genetic type of Duocaima and Quemocuo deposits in the Tuotuohe area in Qinghai Province of China belongs to a typical MVT deposit.The Pb-Zn metallogenic age in the Tuotuohe area is 34?31 Ma,which is defined by the Sm-Nd isotopic isochron age of calcite from the mineralized stage of Duocaima and Quemocuo deposits,along with the age of the Tuotuohe Formation(the youngest ore-bearing horizon).It is proposed a multi-stage mineralization model of the MVT-type Pb-Zn deposits in the fold and thrust belt based on geological characteristics,in-situ analysis for trace elements of sphalerite and S-Pb isotopes of sulfide,and bulk Rb-Sr isotopic compositions of sulfide.In the early stage(Stage 1-2),pyrite framboids and H2S reservoirs were formed by the bacterial sulfate reduction(BSR)in the closed system.Accompanied by the addition of hydrothermal fluid,the metallic ions are combined with light 32S-enriched S2-that was formed by the BSR.Meanwhile,continuously increasing temperature resulted in the initiation of the thermochemical sulfate reduction(TSR),which provided S2-and lead to the formation of the vein-type,brecciated,and disseminated sulfide ores.These ores have depleted Pb and Sr isotopic compositions,along with enriched in 32S,indicating that the ore-forming materials are mainly sourced from the strata,together with possible limited basement materials.In the late stage(Stage 3),under the influence of magmatism,many ore-forming materials were leached from the basement,which mainly gave rise to the disseminated,massive,and brecciated sulfide ores.These ores have enriched Pb and Sr isotopic compositions with various sulfur isotopes.Besides,the sulfur isotopic compositions of some sulfides have higher?34S values than that of coeval seawater,suggesting that the ore-forming materials were derived from both the strata and the basement.Accordingly,it is proposed the prospecting target for the Duocaima deposit should focus on deep faults,interlaminar fracture zone,and other deep favorable ore-hosting space in such deposits.It is proposed that the Duddar deposit in Pakistan belongs to the SEDEX type Pb-Zn deposit with later modification.The metallogenic age of the deposit is 187.8±6.3 Ma,which has been firstly defined by the Re-Os dating of carbonaceous mudstone(ore-bearing host rock).The multi-stage mineralization model of the Duddar Pb-Zn deposit has been established according to geological characteristics,in-situ analysis for trace elements of sphalerite and S-Pb isotopes of sulfides.In the early stage(Stage 1),the deep hydrothermal fluid upwelled along the syngenetic faults,resulting in the formation of stockwork ores,in which S2-is mainly sourced from the seawater or sulfate minerals by the TSR,while the ore-forming materials are mainly derived from the basement.In the late stage(stage 2-4),the hydrothermal fluid was constantly reacting with the metal-rich sediments during the mineralization,so that the laminated and brecciated ores were formed.The S2-of these ores are mainly provided by the seawater sulfate that by TSR and BSR,while the ore-forming materials are mostly derived from the basement and host rocks.The laminated ore recorded the growth process of the pyrite,in which the early sulfides have lower ?34S by BSR,whereas the late sulfides have higher ?34S by TSR.The prospecting target for the Duddar deposit was suggested in this study.It is proposed that the mineralization center of this deposit(north of Exploration line 10740)has the potential to find large ore bodies,and except strengthen the prospect the laminated mineralized bodies in the depth,it should focus on the stockwork mineralized bodies in this prospecting target.(2)Providing new constraints on the tectonic evolution process of Neo-Tethys and its natural resources.It is identified that there are five periods of Pb-Zn mineralization of sediment-hosted Pb-Zn deposits in the Middle-East segment of the Neo-Tethys tectonic domain.Among them,the first period of Pb-Zn mineralization occurred in the extensional stage of Neo-Tethys Ocean,forming SEDEX type deposits in Tianshuihai of China(e.g.,Huoshaoyun deposit),Bela of Pakistan(Duddar deposit),and Hakkari of Turkey.The breakup of Neo-Tethys Ocean continued until 188 Ma in the Middle segment of Tethys domain based on the youngest age of Pb-Zn mineralization.The second period of Pb-Zn mineralization occurred in the subduction stage of the Neo-Tethys Ocean,forming some SEDEX type deposits in Sanandaj of Iran(such as the Mehdiabad deposit).The ore-forming age of these deposits is mainly the Early Cretaceous.It is suggested that the Neo-Tethys Ocean has transferred from the extensional stage into the subduction stage.The third to the fifth period of Pb-Zn mineralization occurred in the continent-continent collision stage of Neo-Tethys,forming MVT type deposits in the whole Tethys domain.Their mineralization ages are 65?55 Ma,41?27 Ma,and 23?11 Ma,which corresponds to the main-collision,late-collision,and post-collision sub-stages respectively,indicating that the continent-continent collision stage of Neo-Tethys has begun from 65 Ma.The SEDEX type Pb-Zn metallogenic belt was extracted from the Middle segment of Neo-Tethys giant MVT-type Pb-Zn metallogenic belt,which provides an important basis for the further Pb-Zn prospecting.It is proposed that the strata formed in the Jurassic and Cretaceous are important host rocks for Pb-Zn deposits.Therefore,it's predicted that the Bela of Pakistan,the southeast Pamir of Tajikistan,and the Hakkari of Turkey are important prospecting targets for Pb-Zn deposits in the Tethys domain in the future.