Trace-element geochemistry and S–O isotopes in the fluorite-barite mineralization of Merguechoum,Moroccan eastern Meseta:insights into ore genesis to the Pangea rifting

The Merguechoum fluorite-barite mineralization,located in the Eastern Meseta of Morocco,is hosted in the Late Hercynian granite.The ore consists of fine crystals of fluorite 1,massive barite 1,euhedral crystals of fluorite 2,and barite 2 with calcite and minor quartz and sulfides.The Merguechoum ore deposits have never been investigated.This study was the first contribution that studied the genesis of fluorite and barite.The ore occurs as dissemination within granite intrusion and also fills the NE-SWtrending meter-sized fractures and faults.The values of the total Rare Earth Elements and Yttrium(REY)and the ratios of LREY/HREY,Y/Ho,Tb/Ca,and Tb/La indicate that the Merguechoum fluorite precipitated from hydrothermal fluids,likely basinal brines,which interacted with the Hercynian granite.The REY data indicate that the ore-forming fluids of the early stage have intensely interacted with the Hercynian granite compared to those of the late ore stage.The gradual decrease in the europium(Eu/Eu^(*)),yttrium(Y/Y^(*)),and cerium(Ce/Ce^(*))anomalies and a low concentration ofΣREY observed in the second ore stage compared to the first ore stage suggest an increase in p H and fO_(2)and by inference a decrease in temperature during the evolution of the hydrothermal system.This evolution could be explained by fluid mixing between the ascending basinal hydrothermal fluids and the diluted sulfate-rich meteoric water barite separates from selected samples reveal that the dissolved sulfates(SO_(4)^(2-))were derived from Permian–Triassic sulfates and/or coeval poreseawater sulfates.The proposed fluid mixing triggered the precipitation of an early-stage F-Ba assemblage followed by the second-stage F-Ba mineralization.Geologic fieldwork,REY inventories,and isotope data point to the ore genesis during the Permian–Triassic extensional tectonic activity concerning the Pangea rifting.This extensional tectonic environment is likely the driving force that mobilized a large amount of the ore-forming basinal brines along the available faults and fractures to the loci of ore deposition.

Zircon Geochronology and Trace Element Geochemistry from the Xiaozhen Copper Deposit, North Daba Mountain: Constraints on Albitites Petrogenesis

Albitite often accompanies with various metal and gem mineral deposits and a large number of occurrences have been reported globally, including the South Qinling orogen, China. The Xiaozhen copper deposit is a typical deposit in the North Daba Mountain area of the South Qinling orogen whose distribution is controlled by albitite veins and fractures. As there are few studies on the petrogenesis of albitite in Xiaozhen copper deposit, this paper focuses on the petrogenesis of albitite and its mineralization age. Detailed fieldwork and mineral microscopic observations initially suggest that albitite from the Xiaozhen copper deposit is igneous in origin. Further zircon trace element geochemistry studies indicate that these zircons have high Th/U ratios（〉0.5）, low La content, high（Sm/La）N and Ce/Ce＊values, and a strong negative Eu anomaly, which are commonly seen in magmatic zircons. The chondrite–normalized rare earth element（REE） patterns are consistent with magmatic zircons from throughout the world, and they fall within or near the field of magmatic zircons on discriminant diagrams. The calculated average apparent Ti–in–zircon temperature for young zircons is 780°C, consistent with magmatic zircon crystallization temperatures. Therefore, zircon geochemistry indicates that the albitite origin is magmatic. SIMS U–Pb dating on nine magmatic zircons yielded a concordia age of 154.8±2.2 Ma, which represents the formation of albitite and the metallogenic age. More importantly, it is consistent with the ages of Yanshanian magmatism and metallogenesis in the South Qinling orogen, so formation of the Xiaozhen copper deposit may be a closely related geological event.

Geochemical Behaviors of REE and Other Trace Elements during the Formation of Strata-bound Skarns and Related Deposits:A Case Study of the Dongguashan Cu(Au)Deposit,Anhui Province,China

REE and other trace elements in the altered marbles, massive skarns and ores, as well as garnet and quartz were determined in order to examine the behaviors of trace elements during hydrothermal alteration. It is demonstrated that the high-field-strength (HFS) elements Zr, Hf, Th and Nb were immobile while other trace elements were mobile during the formation of skarns and related deposits. REE and ore-forming elements such as Cu and Ag in hydrothermally-altered marbles and skarns were provided primarily by hydrothermal fluids. In the direction transverse of the strata, the more deeply the marbles were altered, the higher the total REE abundance and the larger the negative Eu anomalies would be. The chondrite-normalized REE patterns of skarns are similar to those of the marbles, but the former are distinguished by much higher REE contents and more remarkable negative Eu anomalies. Those patterns were apparently not inherited from the marble protolith, but were controlled by garnets, which were determined by the hydrothermal solutions involved in the infiltration metasomatism. The hydrothermal fluids are characterized by having slightly right-hand dipping REE patterns, being enriched in LREE and having strongly negative Eu anomalies. The uptake of REE from hydrothermal fluids during the growth of garnet crystals resulted in the garnets having similar REE patterns to the hydrothermal fluids. Based on the spatial variation of REE in skarns and the structures of the hosting strata, we can get a better understanding of the transport path and pattern of the fluids involved in the formation of skarns and their related deposits. REE geochemistry investigation can help elucidate the genesis of skarns and skarn-related deposits.

Trace Element Geochemistry of Devonian Strata in the Shizhuyuan Ore District, Hunan Province

1 Introduction Both the Qiziqiao Formation and Shetianqiao Formation,which controls the occurrence and distribution of a great deal of metal mineral resources,are extensively developed in southern Hunan province(Liu et al.,1998),showing quite important indicative significance to deep concealed metal mineral resources(Yu et al.,2003).The geochemistry characteristics of Devonian strata could not affect the spatial occurrence shape of orebody

Trace Element Geochemistry of the Baishiquan and Pobei Intrusions,Xinjiang,NW China:Petrogenisis Implications

The Baishiquan and Pobei Early Permian mafic-ultramafic intrusions were emplaced into Proterozoic metamorphic rocks in the Central Tianshan and the Beishan Fold Belt,northern Xinjiang,NW China.The Baishiquan intrusion comprises mainly gabbro,and mela-gabbro sills occur within and along the margins of the gabbro body.In the Pobei intrusion,two distinct gabbroic packages,a lower gabbro and the main gabbro,are intruded and overlain by small cumulate wehrlite bodies.

U-Pb Geochronology and Geochemistry of Stratiform Garnet from the Aqishan Pb-Zn Deposit,Eastern Tianshan,Xinjiang,NW China:Constraints on Genesis of the Deposit

The Aqishan lead-zinc deposit,located in the Jueluotag metallogenic belt of eastern Tianshan,Xinjiang,Northwest China,has a stratiform occurrence in the marine volcanic tuff of the Yamansu Formation.The ore body has a typical double-layer structure,having a stratified,stratoid,lenticular upper part and a veined,stockwork-like lower part.The occurrence of the upper orebody is consistent with that of the volcanic tuff wall rock.The ore minerals are mainly chalcopyrite,pyrite,sphalerite,galena and magnetite,the altered minerals mainly being silicified,such as sericite,chlorite,epidote,garnet.The garnetized skarn,being stratiform and stratoid,is closely related to the upper part of the orebody.Geological observations show that the limestone in the ore-bearing Yamansu Formation is not marbleized and skarnized.Spatially,it is associated with the ferromanganese deposits in the marine volcanic rocks of the Yamansu Formation.These geological features reflect the likelihood that the Aqishan lead-zinc deposit is a hydrothermal exhalation sedimentary deposit.The results from the EPMA show that the garnet is mainly composed of grossular-andradite series,contents being in a range of 34.791-37.8%SiO_(2),32.493-34.274%CaO,8.454-27.275%FeO,0.012-15.293%Al_(2)O_(3),0.351-1.413%MnO,and lower values of 0.013-1.057%TiO_(2).The content of SiO_(2) vs.CaO and FeO vs.Al_(2)O_(3) has a significant positive correlation.The results of ICP-MS analysis for the garnet show that the REE pattern is oblique to right in general.The total amount of rare earth elements is relatively low,ΣREE=71.045-826.52 ppm,which is relatively enriched for LREE and depleted for HREE.LREE/HREE=8.66-4157.75,La_(N)/Yb_(N)=23.51-984.34,with obvious positive Eu and Ce anomalies(δEu=2.27-76.15,δCe=0.94-1.85).This result is similar to the REE characteristics of ore-bearing rhyolite volcanic rocks,showing that the garnet was formed in an oxidizing environment and affected by clear hydrothermal activity.The U-Pb isotopic dating of garnet by fs-LA-HR-ICP-MS gives an age of 316.3±4.4 Ma(MSWD=1.4),which is consistent with the formation time of the Yamansu Formation.According to the study of deposit characteristics and geochemical characteristics,this study concludes that the Aqishan lead-zinc deposit is a hydrothermal exhalation sedimentary deposit,the garnet being caused by hydrothermal exhalative sedimentation.

Rare earth element(REE) geochemistry of different colored fluorites from the Baoshan Cu–Pb–Zn deposit, Southern Hunan,South China

The Baoshan Cu–Pb–Zn deposit, located in the central part of the Qin–Hang belt in South China, is closely related to the granodiorite-porphyry. However, the characteristics and the source of the ore-forming fluid are still ubiquitous. According to the crosscutting relationships between veinlets and their mineral assemblages, three stages of hydrothermal mineralization in this deposit were previously distinguished. In this contribution, two different colored fluorites from the major sulfide mineralization stage are recognized:(1) green fluorites coexisting with Pb–Zn ores;and(2) violet fluorites coexisting with pyrite ores. Y/Ho ratios verify the green fluorites and violet fluorites were co-genetic. The fluorites display elevated(La/Yb)Nratios, which decrease from 1201 to 5710 for green fluorites to 689–1568 for violet fluorites, indicating that they precipitated at the early hydrothermal sulfide stage,and Pb–Zn ores crystallized earlier than pyrite ores. The similar Tb/La ratios of the fluorites also indicate that they precipitated at an early stage within a short time. From the green fluorites to violet fluorites, the total rare earth element(ΣREE)concentrationsdecreasefrom1052–1680 ppm to 148–350 ppm, indicating that the green fluorites precipitated from a more acidic fluid. The Eu/Eu*ratios increase from 0.17 to 0.30 for green fluorites to0.29–0.48 for violet fluorites, and the Ce/Ce* ratios decrease from 1.08–1.13 to 0.93–1.11, suggesting a gradual increase in oxygen fugacity(fO_(2)) and pH value of the mineralization fluid. Though the fluorites display similar REE patterns to the granodiorite-porphyry and limestone,the ΣREE concentrations of the fluorites are significantly higher than those of limestone and the granodiorite-porphyry, suggesting that an important undetected non-magmatic source is involved to provide sufficient REE for fluorites. The most plausible mechanism is fluid mixing between magma fluid and an undetected non-magmatic fluid.

Rutile to Titanite Transformation in Eclogites and its Geochemical Consequences:An Example from the Sumdo Eclogite,Tibet

The formation of titanite coronae after rutile is common in retrograde high-to ultrahigh-pressure meta-mafic rocks,which provides a good opportunity to address the geochemical behavior of HFSE in crustal environments.In the Sumdo eclogite,titanite occurs either as a corona around rutile grains or as semi-continuous veins cross-cutting the major foliation,whereas rutile grains occur either as inclusions in garnet or omphacite or as a relict core surrounded by titanite.Textural relationships and trace elements characteristics of rutile and titanite with different occurrences indicate that both minerals preferentially incorporate Nb and Hf over Ta and Zr in aqueous fluid.Moreover,the breakdown of omphacite and epidote could release substantial amounts of aqueous fluids enriched in Ca,Si,Fe and REE,which would react with rutile to form titanite coronae and veins.During this process,water-insoluble elements,like HFSE and HREE,behave like mobile elements,but they do not migrate substantially out of the system,instead,tending to react in situ.This suggests that the aqueous fluids released during the retrograde metamorphic reactions in mafic rocks could not substantially transfer fluidimmobile elements into the overlying mantle wedge in subduction environments.

Significance of zircon trace element geochemistry,the Shihu gold deposit,western Hebei Province,North China

The Shihu gold deposit is characterized by gold-bearing quartz-polymetallic sulfides and quartz veins.Both Mapeng granitoids batholith and intermediate-basic dikes intruded the metamorphic basement rocks,and are spatially associated with gold mineralization.Trace element abundances in zircons from the Shihu gold deposit,determined by laser-ablation microprobe ICPMS analysis,are sensitive to source rock type and crystallization environment.Concentrations of 21 trace elements were determined for zircons from granitoid rocks,diorites,quartz diorite porphyrites and gold-bearing quartz veins revealed some elemental characteristics and chondrite-normalized trace element patterns from different samples.There were no distinctive differences in REE concentrations of zircons from plutonic rocks and quartz veins,indicating that they probably had the same origin.Relatively flat chondrite-normalized REE patterns with（Yb/Sm）N ratios less than 60 characterized zircons from quartz diorite porphyrites and quartz veins.The highest Nb/Ta ratios were found in zircons from quartz diorite porphyrites,whereas the lowest ratios were found in quartz vein zircons.The Nb/Ta ratios were broadly correlated with HREE＋Y contents,and had weak positive correlations with the depth of the Eu negative anomalies.High values U up to 0.4% and Th up to 0.1%,as well as positive correlations with REE＋Y characterized zircons from quartz vein.The lowest Th/U ratios of zircons present in quartz veins reflected the relatively high concentration of U in hydrothermal fluid,and high Pb concentrations only typified quartz vein grains relatively enriched in U and Th.Zircons from quartz diorite porphyrites showed the most pronounced Ce anomalies,whereas weak Ce anomalies were typical of zircons from quartz veins,in which Eu/Eu＊ of zircons had a broadly negative correlation with Ce/Ce＊.Trace element geochemistry of zircons from mineralized quartz veins and plutonic rocks confirmed that the sources of ore-forming materials were from Precambrian host rocks.Our results significantly enhanced the usefulness of zircon in crustal studies of the North China craton and as an indicator mineral in mineral exploration of the Taihang region.

The petrogenesis of modern and ophiolitic lavas reconsidered:Ti-V and Nb-Th

Tectonic discrimination diagrams are a key tool for understanding ancient volcanic rock origins.In this contribution we compile over 15,000 whole rock compositions to re-evaluate the Ti-V discrimination diagram and compare it to another commonly used tool,the Nb/Yb-Th/Yb diagram.We have reformulated the Ti-V diagram into a log-log plot to distinguish samples more clearly at lower concentrations.The compilation shows that MORB are dominated by Ti/V=20-43,whereas juvenile arc tholeiites and boninites are characterized by Ti/V<20 generally,although there is minor overlap at the boundary(Ti/V=20-22).Plume-related volcanic rocks(ocean island basalts,oceanic plateaux,and continental flood basalts)generally have Ti/V>43,although there may be significant overlap with MORB-like ratios for ridgecentered OIB and for some oceanic plateaux.About 56%of alkaline OIB have Ti/V>70.Back-arc basins are dominantly MORB-like.Melt models show that MORB and juvenile arc volcanics most likely formed under different fO;conditions,but are permissive of similar fO_(2)if the arc rocks form by much higher melt fractions.The Nb/Yb vs.Th/Yb plot clearly distinguishes most oceanic basalts(MORB,plateaux,OIB)from subduction-related volcanic rocks(boninite,juvenile arc tholeiite,calc-alkaline)and from flood basalts.We propose here a new two-proxy diagram of Ti/V vs.Th/Nb,which incorporates the advantages of both.