Geological Characteristics and Genesis of the Jiamoshan MVT Pb–Zn Deposit in the Sanjiang belt, Tibetan Plateau

The carbonate-hosted Pb–Zn deposits in the Sanjiang metallogenic belt on the Tibetan Plateau are typical of MVT Pb–Zn deposits that form in thrust-fold belts. The Jiamoshan Pb–Zn deposit is located in the Changdu area in the middle part of the Sanjiang belt, and it represents a new style of MVT deposit that was controlled by karst structures in a thrust–fold system. Such a karst-controlled MVT Pb–Zn deposit in thrust settings has not previously been described in detail, and we therefore mapped the geology of the deposit and undertook a detailed study of its genesis. The karst structures that host the Jiamoshan deposit were formed in Triassic limestones along secondary reverse faults, and the orebodies have irregular tubular shapes. The main sulfide minerals are galena, sphalerite, and pyrite that occur in massive and lamellar form. The ore-forming fluids belonged to a Mg2+–Na+–K+–SO2-4–Cl-–F-–NO-3–H2 O system at low temperatures(120–130°C) but with high salinities(19–22% NaCl eq.). We have recognized basinal brine as the source of the ore-forming fluids on the basis of their H–O isotopic compositions(-145‰ to-93‰ for δDV-SMOW and-2.22‰ to 13.00‰ for δ18 Ofluid), the ratios of Cl/Br(14–1196) and Na/Br(16–586) in the hydrothermal fluids, and the C–O isotopic compositions of calcite(-5.0‰ to 3.7‰ for δ13 CV-PDB and 15.1‰ to 22.3‰ for δ18 OV-SMOW). These fluids may have been derived from evaporated seawater trapped in marine strata at depth or from Paleogene–Neogene basins on the surface. The δ34 S values are low in the galena(-3.2‰ to 0.6‰) but high in the barite(27.1‰), indicating that the reduced sulfur came from gypsum in the regional Cenozoic basins and from sulfates in trapped paleo-seawater by bacterial sulfate reduction. The Pb isotopic compositions of the galena samples(18.3270–18.3482 for 206 Pb/204 Pb, 15.6345–15.6390 for 207 Pb/204 Pb, and 38.5503–38.5582 for 208 Pb/204 Pb) are similar to those of the regional Triassic volcanic-arc rocks that formed during the closure of the Paleo-Tethys, indicating these arc rocks were the source of the metals in the deposit. Taking into account our new observations and data, as well as regional Pb–Zn metallogenic processes, we present here a new model for MVT deposits controlled by karst structures in thrust–fold systems.

Geological significance of nickeliferous minerals in the Fule Pb–Zn deposit, Yunnan Province, China

Abstract The Fule Pb-Zn deposit is located in the Sichuan-Yunnan-Guizhou Province, and it is an important and giant low temperature metallogenic domain in China. In our research area, the Pb-Zn deposits are mainly hosted in the Permian Yangxin Formation and are composed of dolostone and limestone. The distance between the ore bodies and the Permian Emeishan basalt ranged from 50 to 160 m. In this study, the nickel rich minerals, including vaesite, polydymite and millerite, were reported for the first time in the Fule deposit. These minerals occurred as xenomorphic mineral aggregate and were sporadically distributed in the sphalerite-galena-calcite vein, which is the main ore type in the deposit. Our study indicated that the paragenetic sequence of minerals in the Fule deposit is the following order： polydymite → vaesite → mil- lerite → sphalerite → galena → tetrahedrite （tennantite）. The geological occurrence characteristics of those nicke- liferous minerals suggested that the Permian Emeishan basalt is a possible barrier layer of Pb-Zn ore-forming fluid, and it is an important source for the Ni and part of the Cu in the deposit. The Sichuan-Yunnan-Guizhou Pb-Zn mineralization province is a world-class production base of Pb and Zn, in which the Permian Emeishan basalt and Pb- Zn deposits have uniformly spatial distribution, but the relationship of mineralization between them is still under debate. This report provides new evidence for understanding the relationship between Pb-Zn mineral- ization and Permian Emeishan basalt in the Sichuan- Yunnan-Guizhou Pb-Zn mineralization province.

Trace Elements in Sphalerite from the Dadongla Zn-Pb Deposit, Western Hunan-Eastern Guizhou Zn-Pb Metallogenic Belt, South China

The western Hunan-eastern Guizhou Zn-Pb metallogenic belt is one of the important Zn-Pb mineralization regions in China.The Dadongla deposit,located in the northeast of Guizhou Province,is one of the typical Zn-Pb deposits in the region and has estimated resources more than 12 million metric tons(Mt)with an average grade of 4.11 wt%Zn+Pb.Its orebodies are hosted in the lower Cambrian Aoxi Formation dolomite,occurring as bedded,para-bedded in shape,and in conformity with the wall rock.The ore mineral assemblage is simple,dominated by sphalerite with minor pyrite and galena,and the gangue minerals are composed of dolomite,calcite with minor bitumen and barite.In view of the lack of geological and geochemical researches,the genesis of Zn-Pb ore is still unclear.Laser ablation-inductively coupled plasma mass spectrometry(LA-ICPMS)spot and mapping analyses were used to obtain sphalerite trace element chemistry in the Dadongla Zn-Pb deposit in Guizhou,China,aiming to constrain its ore genesis.The results show that sphalerite is characterized by the enrichment of Cd,Fe,Ge and Hg,corresponding with that of typical MVT deposits.Four zones were identified in the sphalerite crystal from Dadongla from the center to margin according to the color bands.in which the zone in the center,representing the early ore-stage sphalerite,is characterized by enrichment of Cd relatively,while the zone forming at late ore-stage is enriched in Ge and Hg relatively.The finding was controlled by differential leached metals content in ore-forming fluid from its source rock.Notably,critical element Ge trends to be enriched at the late ore-stage and follows a substitution of 2 Zn^2+(?)Ge^4++□(vacancy).Moreover,the calculated ore-forming temperature ranges from 79.9℃to 177.6℃by the empirical formula,which is similar to that of typical Mississippi Valley-type(MVT)deposits.Compared with the features of trace elements in sphalerite from different types of deposits,together with the geology,the Dadongla deposit belongs to an MVT Zn-Pb deposit.

3D Modeling and Determination of Factors Responsible for Zinc-Lead Mineralization in the Mehdiabad Deposit,Central Iran,based on Statistical Analysis of Geochemical Data

Although the Mehdiabad zinc-lead deposit is one of the most well-known deposits in the central Iran structural zone,the genesis of the deposit remains controversial.The host rock of the ore is a dolomitic limestone of the Lower Cretaceous Taft Formation.In the two main orebodies of the deposit,which includes the Black Hill and East Ridge ore zones,the oxide and sulfide ores are observed at the surface and at depth,respectively.The elements Zn,Fe,Mn and Mg are more abundant in the East Ridge ore zone(in both sulfide and oxide ores),with Ba,Pb,Ag and Cu being more abundant in the Black Hill oxide ore.Based on the distribution of elements and their correlation with each other in these ore zones,the elements are divided into three general groups,that of terrigenous elements,chemically-deposited elements and oreforming(hydrothermally deposited)elements,a division that is supported by the results of factor analyses.The spatial distribution of elements is jointly affected by contact with host rocks,the boundary of oxide-sulfide ores and fault zones.The main factors governing the distribution of elements are the mechanical transfer of detrital sediments,chemical sedimentation,transfer by hydrothermal fluids,oxidation and surface dissolution,all of which affected the spatial distribution of elements.The ore-forming elements are mostly affected by hydrothermal fluids and oxidation.This study not only provides additional information about the genesis of the Mehdiabad deposit,but also could assist in the exploitation of ore and further exploration purposes.The results of this study can aid in the exploration and exploitation of the Mehdiabad deposit and similar deposits in the region.

Thermochemical sulphate reduction and Huayuan lead-zinc ore deposit in Hunan, China

In recent years, some arguments with regard to the organicmineralization of MVT lead-zinc ore deposit are focused on the thermochemical sulphate reduction in the presence of organic matter. Based on the research into the organic geochemistry and C, O, S isotopes of mineralized host rocks, mineral gas fluid inclusion and solid bitumen from Huayuan (W. Hunan, China) lead-zinc ore deposit formed in the algal limestones of Qingxudong formation, Lower Cambrian, the authors consider that a lot of organic matter occurred and participated in mineralization. The organic matter from different sources participated in the mineralization with two main forms: thermochemical sul-phate reduction and thermal degradation which supplied abundant H2S for the precipitation.

Palynological constraints on the age of the Mississippi Valley-type Changdong Pb-Zn deposit,Sanjiang belt,West China

Mississippi Valley-type(MVT)Pb-Zn deposits serve as the world’s major supply of Pb-Zn resources.However,the age constraint of MVT Pb-Zn deposits has long been a big challenge,due to the lack of minerals that are unequivocally related to ore deposition and that can be used for radioisotopic dating.Here we show sporopollens can provide useful chronological information on the Changdong MVT Pb-Zn deposit in the Simao basin,Sanjiang belt,West China.The Pb-Zn ores in the Changdong deposit are hosted by internal sediments in paleo-karst caves of meteoric origin.Sphalerite and galena occur as replacements of carbonate minerals and void infillings in the internal sediments.The relations suggest that the Pb-Zn mineralization occurred after the deposition of the internal sediments.A palynological assemblage mainly composed of angiosperm pollen dominated by Castanea,Quercus,and Carya and fern spores dominated by Polypodiaceae,Pteris,and Athyriaceae was identified.These pollen and spores place the ore-hosting internal sediments and the Changdong paleo-karst at early to middle Oligocene.Consequently,the Changdong Pb-Zn deposit must have formed after the early Oligocene(~34 Ma).These age constraints,together with the geological characteristics,indicate that the Changdong Pb-Zn deposit is a paleo-karst-controlled MVT deposit related to fold-thrust systems in the Sanjiang belt.The Changdong deposit is similar to other MVT Pb-Zn deposits in the northern part of the Sanjiang belt,making it possible to extend this Pb-Zn belt 500 km further to the South.Results presented here highlights the potential of sporopollens in dating the age of MVT deposits related to paleo-karst formation in young orogenic belts.