Infrared microthermometry of fluid inclusion in sphalerite:A case study of the Xinqiao deposit in the Middle-Lower Yangtze metallogenic belt

Infrared microthermometry allows direct measurement of fluid inclusions hosted in opaque ore minerals and can provide direct constraints on the evolution of ore-forming fluids.This study presents infrared microthermometry of spherite-hosted fluid inclusions from the Xinqiao deposit in the Middle-Lower Yangtze Metallogenic Belt and sheds new light on the ore genesis of the deposit.Considering that infrared light may lead to non-negligible temperature deviations during microthermometry,some tests were first conducted to ensure the accuracy of the microthermometric measurements.The measurement results indicated that using the lowest light intensity of the microscope and inserting an optical filter were effective in minimizing the possible temperature deviations of infrared microthermometry.All sphalerite-hosted fluid inclusions from the Xinqiao deposit were aqueous.They show homogenization temperature ranging from~200 to 350℃,but have two separate salinity groups(1.0 wt%-10 wt%and 15.1 wt%-19.2 wt%NaCl equivalent).The low-salinity group represents sedimentary exhalative(SEDEX)-associated fluids,whereas the high-salinity group results from modification by later magmatic hydrothermal fluids.Combined with published fluid inclusion data,the four-stage fluid evolution of the Xinqiao deposit was depicted.Furthermore,our data suggest that the Xinqiao deposit was formed by twostage metallogenic events including SEDEX and magmatic-hydrothermal mineralization.

Fluid Inclusion Petrography and Microthermometry of Zn and Pb Deposits of Rajpura-Dariba Bethumni Belt, Udaipur District (Rajasthan), India

The Proterozoic Aravalli-Delhi orogenic complex hosts a large number of economically important stratabound base metal sulphide deposits. In the present work, rock samples taken from Outcrop and Underground Mine of Sindeskar Kalan, Vedanta Group, Rajpura Dariba-Bethumni Belt which is located at a distance of 76 kms from Udaipur city, Rajasthan have been studied. The chief litho units of the group which contain sulfide-bearing calc-silicate and graphite mica schist, dolomite marble, calc-biotite schist and quartzite are identified. An attempt has also been made to study/or hydrothermal in origin in the different types of fluid inclusions, hosted predominately in Geothermometry viz. heating and freezing study of entrapped palaeo-fluids (such as sedimentary and quartz host grain and a few in sphalerites). The quartz hosts are identified with four types of fluid inclusions, such as 1) monophase (gas/vapour), 2) gas-rich biphase, 3) liquid-rich biphase and 4) polyphase types. The primary types of fluid inclusions show that melting temperature of ice or depression freezing point (DFP) (ranging from -2.5°C to -7.2°C)/(salinity ranging from 4.5 - 13.25 wt% NaCl eq.) and temperature of homogenization into liquid phase (ranging from +188°C to +218°C) have been measured. Data from the fluid inclusions and salinity calculation (low salinity) reveal that rate of cooling is the important mechanism of ore deposition in the study area.

Cu-Bearing Mokama Granite Prospect of the Kibara Belt in the Maniema Province, DRC: A Preliminary Petrography, Geochemistry, and Fluid Inclusion Study

The Mokama granites are located in the Kibara belt (KIB) and hosts tin oxide group minerals (TOGM: Sn-W), and sulfide group minerals (SGM: Cu-Zn-Fe-As). The essential of Cu mineralization (non-economic deposit) is disseminated inside the rock and consists of minerals (Raman, EPMA and metallographic microscopy) including chalcopyrite and bornite that are replaced by chalcocite and covellite, and the last also replaced later by malachite. The chemistry (XRF, LA-ICP-MS) of these peraluminous S-type leucogranites show SiO2 (71 wt% - 79 wt%), ASI (1.4 - 3.1 molar), and are enriched in Rb (681 - 1000 ppm), Ta (12–151 ppm), Sn (43 - 142 ppm), Cu (10 - 4300 ppm), Zn (60 - 740 ppm), U (2.2 - 20.7 ppm) while depleted in Zr (20 - 31 ppm), Sr (20 - 69 ppm), Hf (1.3 - 2.0 ppm), Th (2.2 - 18.9 ppm), W (9 - 113 ppm), Pb (5 - 50 ppm), Ge (5 - 10 ppm), Cs (21 - 53 ppm) and Bi (0.6 - 17.4 ppm) and low ratios of (La/Yb) N, (Gd/Yb) N, (La/Sm) N). Fluid inclusion assemblages (FIAs) hosted in quartz in the Mokama granites show ranges of salinities of 4 - 23 wt% (NaCl equivalent) and homogenization temperatures (Th) of 190°C - 550°C. A boiling assemblage in the granite suggests a fluid phase separation occurred at about 380 - 610 bars, and this corresponds to apparent paleodepths of approximately 1 - 2 km (lithostatic model) or 3 - 5 km (hydrostatic model). FIAs hosted in TOGM such as cassiterite (salinities of 2 wt% - 10 wt% and Th of 220°C - 340°C) helped set up the possible temperature limit of SGM (Cu sulfide) precipitations that are estimated below 200°C.

Ore-forming Fluid and Metallogenic Mechanism of Wolframite-Quartz Vein-type Tungsten Deposits in South China

South China is endowed with copious wolframite-quartz vein-type W deposits that provide a significant contribution to the world‘s tungsten production.Mineralization is spatially associated with highly evolved granites,which have been interpreted as products of ancient crustal anatexis.Ore veins are mainly hosted in low-grade metamorphosed quartz sandstone,slate and granitic rocks.The ore minerals mainly comprise wolframite,cassiterite,scheelite and pyrite,with minor molybdenite,arsenopyrite and chalcopyrite.Typical steeply dipping veins can be divided into five zones from top to the bottom,namely:(Ⅰ)thread,(Ⅱ)veinlet,(Ⅲ)moderate vein,(Ⅳ)thick vein,and(Ⅴ)thin out zones.In general,three types of fluid inclusions at room temperature are commonly recognized in wolframite and/or quartz from these veins:two-phase liquid-rich(type L),two-phase CO2-bearing(type CB),and CO2-rich(type C).Comparative microthermometry performed on fluid inclusions hosted in wolframite and associated quartz indicates that most wolframite was not coprecipitated with the coexisting quartz.Detailed petrographic observation and cathodoluminescence(CL)imaging on coexisting wolframite and quartz of the Yaogangxian deposit,show repeated precipitation of quartz,wolframite,and muscovite,suggesting a more complex fluid process forming these veins.Previous studies of H-O isotopes and fluid inclusions suggested that the main ore-forming fluids forming the wolframite-quartz vein-type deposits had a magmatic source,whereas an unresolved debate is centered on whether mantle material supplemented the ore-forming fluids.The variable CO2 contents in the ore-forming fluids also implies that CO2 might have had a positive effect on ore formation.Fluid inclusion studies indicate that wolframite was most likely deposited during cooling from an initial H2 O+Na Cl±CO2 magmatic fluid.In addition,fluid-phase separation and/or mixing with sedimentary fluid might also have played an important role in promoting wolframite deposition.We speculate that these processes determine the precipitation of W to varying degrees whereas the leading mechanistic cause remains an open question.Comprehensive studies on spatial variation of fluid inclusions show that both the steeply and gently dipping veins are consistent with the"five floors"model that may have broader applications to exploration of wolframite-quartz vein-type deposits.Recent quantitative analysis of wolframite-and quartz-hosted fluid inclusions by laser ablation inductively-coupled plasma mass spectrometry shows enhanced advantages in revealing fluid evolution,tracing the fluid source and dissecting the ore precipitation process.Further studies on wolframite-quartz vein-type W deposits to bring a deeper understanding on ore-forming fluids and the metallogenic mechanism involved.

Mineralogy,sulfur isotopes and infrared microthermometric study of the Leishan-Rongjiang antimony ore field,SW China

The Leishan-Rongjiang antimony ore field(LAOF) is in a unique geotectonic location in the uplift between the Youjiang and Xiangzhong basins.This paper focuses on two representative deposits in the LAOF:the Bameng and Peize antimony(Sb) deposits.We analyzed fluid inclusions(FIs) in stibnite and coexisting quartz,as well as the sulfur isotopic composition of stibnite,to better understand the nature of the ore-forming fluid and the metallogenic process.The FIs data from samples of the stibnite and coexisting quartz indicate that the ore-forming fluids were characterized by low-temperature(150-210 ℃),low-salinity(1.5 wt%-6.0 wt%NaCl equiv.),and low-density(0.872-0.961 g/cm^3).The δ^(34)S values of stibnite(-8.21‰ to 3.76‰,average =-6.30‰)fall in between the sulfur isotopic compositions of the mantle and of biogenic sulfur in sedimentary rocks.However,the δ^(34)S_(∑s) values(-4.41 ‰ to +0.04‰,average =-2.49‰) of the ore-forming fluids are generally closer to the sulfur isotopic composition of the mantle source,indicating that the sulfur in the LAOF was mainly sourced from the mantle,but with possible involvement of biogenic sulfur.In addition,FIs petrography and ore deposit geology show that fluid boiling resulted from an abrupt decrease in pressure,which may have triggered the precipitation of stibnite.We conclude that low-temperature,dilute hydrothermal fluids with mixed origins migrated along the regional fault and interacted with the wall rock,extracting the ore-forming materials.Then,the oreforming fluids were injected into the fault fracture zones.

Determination of Salinity in Fluid Inclusions with Laser Raman Spectroscopy Technique

A preliminary study was conducted to outline the laser Raman spectroscopy technique for determination of salinity in the aqueous phase in fluid inclusions. The skewing parameters of the Raman profiles of the calibration solutions determined were used to derive a calibration curve for the estimation of the equivalent mass fraction NaCl in aqueous solutions. This technique was also verified in the analysis of the natural fluid inclusions from Tongshankou porphyry Cu (Mo) deposit, Hubei Province, China. Although the analyses on the natural fluid inclusions are limited, an acceptable agreement has been reached on the salinities, for most fluid inclusions, determined by the Raman spectroscopy and microthermometry techniques, indicating the reliability of the Raman technique for determination of salinity in fluid inclusion studies.

Fluid inclusion studies of the Kenticha rare-element granite-pegmatite,Southern Ethiopia

In the Kenticha area,a series of barren to rare metal-bearing pegmatites intruded into the Neoproterozoic Adola Belt.The pegmatites host world-class Nb and Ta deposits and significant Li and Be reserves.In this contribution,fluid inclusion data and feldspar geothermometry have been combined to define the crystallization condition of the Kenticha rare-metal pegmatite.Primary and complex assemblages of secondary fluid inclusions representing episodic fluid circulations have been identified in quartz and spodumene.A primary aqueous-carbonic fluid of low salinity aqueous solution with liquid and vapour CO_(2) phases,secondary carbonic fluid rich and carboniconly fluids,and multiple generations of secondary aqueous inclusions that represent sub-solidus hydrothermal circulation have been identified.All aqueous inclusions were homogenized into the liquid phase between 100 and 290℃.Aqueous-carbonic inclusions were homogenized,usually via a critical transition[T_(h)(LV→SCF)]between 241 and 397℃,or less commonly,via a dew-point transition[T_(h)(LV→V)]between 213 and 264℃.Crystallization of the rare-element pegmatite is certainly associated with the late-stage magmatic or early hydrothermal low-salinity aqueous-carbonic fluid that homogenizes to critical conditions.A combination of microthermometric data and existing experimentally determined solidus from flux and volatile bearing haplogranite suggests exsolution of fluids from hydrous silicate melt,perhaps during crystallization of the aplitic layer.The fluids were then trapped and isobarically cooled along a reasonable geothermal gradient within the pegmatite unit down to a temperature of around 397℃.

Genesis of the Xinfang Gold Deposit,Liaodong Peninsula:In-sights from Fluid Inclusions and S-Sr Isotopic Constraints

The North China Craton(NCC)has been continuously reactivated since the Mesozoic and this decratonization is responsible for its economically important gold mineralization in the Meso-zoic.The Early Cretaceous(110-130 Ma)gold mineralization in the NCC has been well-studied due to its significance,but little attention has been given to other episodes of gold mineralization related to polyphased reactivation of the NCC.The Xinfang mesozonal gold deposit(143 Ma)in the Liaodong Peninsula is related to the one of the episodes of the Yanshanian orogeny.The orebodies of the Xin-fang gold deposit were controlled by the low angle transpressive fault systems and hosted by the Neoarchean monzogranitic gneiss.Fluid inclusion microthermometry reveals that the mineralizing temperatures range from 220 to 280℃,with salinities from 6 wt.%NaCl eqv.to 15 wt.%NaCl eqv.,pressures from 199 to 321 Ma.The S isotopic characteristics of sulfides not only record a heterogene-ous source including magmatic or gneissic sulfur but also record inter-mineral isotope fractionation.The initial^(87)Sr/^(86)Sr values of pyrite(0.713480-0.729031)indicate a radiogenic crustal origin for the sources.The metamorphic dehydration of the underlying basement resulted in the genesis of the Xin-fang gold deposit.We summarize three episodes of gold mineralization in the Liaodong Peninsula re-lated to continuous reactivation of the NCC,which indicates a great exploration potential of this area.