Hydrothermal Mineralization Processes Research Articles

Anatomy of a fumarole field: drone remote-sensing and petrological approaches reveal the degassing and alteration structure at La Fossa cone, Vulcano, Italy

Abstract. Hydrothermal alteration and mineralization processes can affect the physical and chemical properties of volcanic rocks. Aggressive acidic degassing and fluid flow often also lead to changes in the appearance of a rock, such as changes in surface coloration or intense bleaching. Although hydrothermal alteration can have far-reaching consequences for rock stability and permeability, limited knowledge exists on the detailed structures, extent, and dynamic changes that take place near the surface of hydrothermal venting systems. By integrating drone-based photogrammetry with mineralogical and chemical analyses of rock samples and surface gas flux, we investigate the structure of the evolving volcanic degassing and alteration system at the La Fossa cone on the island of Vulcano, Italy. Our image analysis combines principal component analysis (PCA) with image classification and thermal analysis through which we identify an area of approximately 70 000 m2 that outlines the maximum extent of hydrothermal alteration effects at the surface, represented by a shift in rock color from reddish to gray. Within this area, we identify distinct gradients of surface coloration and temperature that indicate a local variability in the degassing and alteration intensity and define several structural units within the fumarole field. At least seven such larger units of increased activity could be constrained. Through mineralogical and geochemical analysis of samples from the different alteration units, we define a relationship between surface appearance in drone imagery and the mineralogical and chemical composition. Gradients in surface color from reddish to gray correlate with a reduction in Fe2O3 from up to 3.2 % in the unaltered regime to 0.3 % in the altered regime, and the latter coincides with the area of increased diffuse acid gas flux. As the pixel brightness increases towards higher alteration gradients, we note a loss of the initial (igneous) mineral fraction and a change in the bulk chemical composition with a concomitant increase in sulfur content from close to 0 % in the unaltered samples to up to 60 % in samples from the altered domains. Using this approach of combined remote-sensing and in situ analyses, we define and spatially constrain several alteration units and compare them to the present-day thermally active surface and degassing pattern over the main crater area. The combined results permit us to present a detailed anatomy of the La Fossa fumarole field, including high-temperature fumaroles and seven larger units of increased alteration intensity, surface temperature, and variably intense surface degassing. Importantly, we also identify apparently sealed surface domains that prevent degassing, likely as a consequence of mineral precipitation from degassing and alteration processes. By assessing the thermal energy release of the identified spatial units quantitatively, we show that thermal radiation of high-temperature fumaroles accounts for < 50 % of the total thermal energy release only and that the larger part is emitted by diffuse degassing units. The integrated use of methods presented here has proven to be a useful combination for a detailed characterization of alteration and activity patterns of volcanic degassing sites and has the potential for application in alteration research and for the monitoring of volcanic degassing systems.

Effects of Metasomatism on Granite-Related Mineral Systems: A Boron-Rich Open Greisen System in the Highiş Granitoids (Apuseni Mountains, Romania)

Greisenization is typically linked with highly fractionated granites and is often associated with hydrothermal vein systems. Late to postmagmatic metasomatic processes involve the enrichment of volatile components such as boron and halogens as well as several metallic elements. The purpose of this study is to reveal the main metasomatic effects and paragenetic sequences of the related mineralizations in Highiş granitoids, Romania. In a natural outcrop, more than 30 samples were collected from granitoids, felsic veins, and country rocks. We carried out a detailed mineralogical and petrological characterization of carefully selected samples using X-ray powder diffractometry, electron microprobe analysis, and microscopic methods together with K–Ar ages of whole rocks and K-bearing minerals. Several characteristic features of albitization, sericitization, tourmalinization, epidotization, and hematitization were recognized in the studied samples. Crystallization of quartz, K-feldspar, and magnetite represents the first stage during the magmatic-hydrothermal transition. The mineral assemblage of albite, sericite, schorl, and quartz originates from the early and main stages of greisenization. While the subsequent mineral assemblages, which predominantly include dravite, specular hematite, and epidote, are closely related to the late vein-depositing stage. We propose that the study area could belong to a boron-rich open greisen system in the apical portion of Guadalupian A-type granite. Based on a new hypothesis, the previously published Permian crystallization ages (between ~272 Ma and ~259 Ma) could be homogenized and/or partially rejuvenated during the hydrothermal mineralization processes due to uraniferous vein minerals. Additionally, the Highiș granite-related system suffered a Cretaceous thermal overprint (between ~100 Ma and ~96 Ma). The results may help to understand the evolution of highly evolved granite intrusions worldwide and improve our knowledge of the effect of hydrothermal mineralization processes on the emplacement ages.

Mantle plume plays an important role in modern seafloor hydrothermal mineralization system

Deyin-1 hydrothermal field is located on the Southern Mid-Atlantic Ridge (SMAR) 15°S. The geochemical characteristics of substrate basalts record the incorporation of Saint Helena plume components in the magma source, which implies that the hydrothermal mineralization characteristics in Deyin-1 might be influenced by the mantle plume indirectly. In this study, the pyrite trace element contents and sulfide in situ Pb and He-Ar isotope compositions of a chimney sample from Deyin-1 field are determined systematically in order to clarify the mantle plume influence on local hydrothermal mineralization process. The higher Ba/Co ratios in Deyin-1 pyrites, compared with those from other mid-ocean ridge hydrothermal fields, may be related to the Saint Helena mantle plume influence. Besides, Deyin-1 pyrites possess lower Pb/As, Ag/As, Ni/As ratios and higher As contents than ultramafic-hosted hydrothermal fields, indicating the Deyin-1 is a mafic-hosted hydrothermal system. The higher Se, Co and lower Zn, As, Pb contents in pyrites from interior layers of the chimney demonstrate that the fluid temperature increases during the chimney growth. The in situ Pb isotope compositions of Deyin-1 sulfides are similar to those of mantle plume-influenced basalts in SMAR 15°S and more radiogenic than that of the plume-free SMAR basalt, which demonstrates that the Saint Helena mantle plume has contributed parts of Pb (and other metal elements) to the Deyin-1 sulfides. The He isotope compositions of Deyin-1 sulfides also prove the mantle plume contribution to the hydrothermal system. End-member mixing calculation of Pb-He isotopes indicates that the Saint Helena plume components account for about 3% of the mineralization material sources in Deyin-1 sulfides. Many hydrothermal fields have been discovered near the hot spots besides Deyin-1. Our study emphasizes that mantle plume influence on hydrothermal mineralization might be ubiquitous and needs to be revaluation. This study might shed some light on modern seafloor hydrothermal mineralization process and lithosphere-seawater mass exchange.

Two-stage enrichment of germanium in the giant Maoping MVT Pb-Zn deposit, southwestern China: Constraints from in situ analysis of multicolor sphalerites

The Maoping Pb-Zn deposit is one of the largest deposits in the Sichuan-Yunnan-Guizhou (SYG) MVT province in southwest China, which is also one of the biggest germanium producers in China. The hydrothermal mineralization process in this deposit can be divided into: (I) dolomite-pyrite stage, (II) sphalerite-galena stage, and (III) calcite stage. Five colors of sphalerites are recognized, including (C1) black, (C2) red brown, (C3) deep brown, (C4) light brown, and (C5) light red sphalerite. Pure colored C1, C2, C3 and C4 are dominanting in the entire sphalerite sequence, and there are also few rhythmic zonal sphalerites (e.g., Z1, Z2) composed of above four colored sphalerites. The C5 sphalerite precipitates last, and often cross-cuts other colored sphalerites in fine veins. Galena usually postdates than multicolor sphalerites. Based on μ-XRF and LA-ICP-MS mapping analysis, the Fe and Cu respectively dominate the variations of many other trace elements (e.g., Mn, Ag, Cd, Ga, Ge). The C5 and C1 sphalerites show the highest germanium contents (geometric mean 49 ppm for C5; 22 ppm for C1), followed by C4 (geometric mean 13 ppm). The contents of germanium and copper show a strong linear correlation for all colored sphalerites, in which germanium incorporates into sphalerite by the mechanism of 2Cu+ + Ge4+ → 3Zn2+, while the nano-inclusion of Cu(Ag)-As(Ga)-S sulfosalt may evenly distribute in C5 sphalerite, resulting in its higher (Cu/Ge)mol ratios. According to the temperature and sulfur fugacity deduced from element compositions of sphalerite, the higher sulfur fugacity is more beneficial to the enrichment of germanium, relative to temperature. The sulfur isotope data suggest that the sulfur in C1, C2, C3 and C4 sphalerites originated from the Zaige and Baizuo Formations via bacterial sulfide reduction (BSR), in contrast to the sulfur in C5 sphalerite that mainly derived from the Datang Formation, with significantly higher sulfur fugacity and lower temperature. It is concluded that the fluids with germanium and reduced-sulfur derived from the Zaige and Baizuo Formations, mixed with the metal-bearing (e.g., Pb, Zn, Ag) basin brine, and caused the first-stage germanium enrichment in C1, C2, C3 and C4 sphalerites. Then the second-stage enrichment of germanium in C5 sphalerite was due to the involvement of fluid with germanium and reduced-sulfur derived from the Datang Formation.

Fe-Pb-Sr isotopic systematics of the hydrothermal chimney from the Minami-Ensei hydrothermal field, middle Okinawa Trough: Constraint on hydrothermal mineralization process in incipient back-arc basin

The study of hydrothermal chimney from the Okinawa Trough (OT) is of important significance for uncovering the hydrothermal mineralization characteristics in incipient back-arc basins. Although many researches have been conducted on OT hydrothermal sulfides, the mineralization processes in this region are still unclear. In this paper, Sr-Pb-Fe isotope compositions of a hydrothermal chimney from the Minami-Ensei (ME) hydrothermal field, middle Okinawa Trough, are analyzed systematically in order to clarify the mineralization process in this field. The hydrothermal fluid has interacted with overlying sediment during the hydrothermal circulation. What is noteworthy is that the Sr and Pb isotope compositions of ME sulfides are less radiogenic than those of other OT fields, which is caused by the weaker fluid/sediment interaction and less leaching of sediment components under lower fluid temperature condition in ME. The δ56Fe values of ME pyrites range from −0.52 to −1.05 ‰, which is apparently lower than that of parental fluid (−0.10 to −0.30 ‰). During pyrites crystallization, strong Fe isotope kinetic fractionation occurs, resulting in the negative shifts in pyrite δ56Fe values. Although bacterial sulfate reduction occurred throughout the whole mineralization process, its influence on Fe isotope kinetic fractionation is negligible. This is because the production of bacterial H2S is limited in ME, which cannot influence the pyrite crystallization rates (i.e., the degrees of Fe isotope kinetic fractionation) remarkably. This research is helpful for shedding light on mineralization processes in incipient back-arc basin hydrothermal fields.

Textural and LA-ICP-MS trace element analyses reveal co-enriched Au-Sb-W metallogeny in the Woxi deposit, west Jiangnan Orogen, South China

It is well-known that tungsten and antimony are commonly enriched in the gold deposit and occur as Au-Sb or Au-W deposits. However, the Woxi deposit, located in the West Jiangnan Orogen of South China, is remarkably co-enriched in the Au-Sb-W elemental association. This deposit is characterized by multistage Au mineralization and reactivation of structures developed in the Neoproterozoic metamorphic rocks, but the detailed mechanism of its co-enriched Au-Sb-W metallogeny is still unclear. Here, we perform detailed petrographic observations and ore mineral textural and pyrite compositional analyses by using SEM and LA-ICP-MS to constrain ore-forming physiochemical conditions and to decipher the Au-Sb-W metallogenic mechanism in the Woxi deposit. The Woxi deposit consists of nine auriferous quartz lodes in the shape of stratiform, tabular, and lenticular, which are surrounded by alteration halos in the Neoproterozoic slate. These orebodies are distributed along the bedding-parallel fracture zones of the EW-striking and N-dipping in the purplish red slate of the Madiyi Formation, below the regional EW-striking Woxi fault. Four stages of hydrothermal mineralization and alteration processes could be recognized in the Woxi. Stage 1 occurs in bleached slate, and consists of euhedral, porous, and coarse auriferous pyrite (Py1), with slight arsenopyrite, siderite, and rutile. Stage 2 mainly consists of subhedral to euhedral and compositional zoning auriferous pyrite (Py2) and scheelite (Sch1), with slight wolframite and apatite hosted in quartz veinlets and native gold enclaved in Sch1. Stage 3 is characterized by scheelite (Sch2) and stibnite, with slight native gold and dendritic-shaped anhedral auriferous pyrite (Py3) hosted in quartz veins. Stage 4 features a quartz-calcite-barite-chlorite mineral assemblage that occurred as veinlets, or in the pressure shadows of Py1. Gold is mainly incorporated in the three stages (S1 to S3) of arsenian pyrite (Py1to Py3) as invisible gold and, to a lesser extent, formed visible native gold at late S2 and S3, tungsten mineralization occurs mainly as scheelite (Sch1) and wolframite at S2, with a minor amount of scheelite (Sch2) at S3, and antimony mineralization is mainly occurred as stibnite at S3. Furthermore, invisible gold most likely occurs as nanoscale particles of Au-Bi-Pb-bearing tellurides in Py1, and may be hosted in the structurally bounded lattice of Py2 and Py3.The SEM study presents highly developed dissolution-reprecipitation microstructures in hydrothermal minerals, such as pyrite, arsenopyrite, wolframite, scheelite, and apatite. Mineral paragenesis and pyrite trace element signatures suggest the ore fluid is characterized by elevated fO2, low pH and high temperature in S1, decreased fO2, medium pH and medium temperature in S2, and elevated fO2, high pH and low temperature in S3. The evolution of the physicochemical condition may be induced by penetration of multipulse ore-forming fluids and the transition of the ore-forming mechanism from fluid-rock interaction in S1 and early S2 to phase separation in late S2 and S3, as suggested by textural and LA-ICP-MS analyses. This study highlighted that coupled dissolution-reprecipitation reactions might facilitate the association of the Au-Sb-W elemental that successively mineralized and co-enriched in the Woxi deposit.

Origin of the Woxi orogenic Au-Sb-W deposit in the west Jiangnan Orogen of South China: Constraints from apatite and wolframite U-Pb dating and pyrite in-situ S-Pb isotopic signatures

The majority of gold mineralization in the Jiangnan Orogenic Belt (JOB) of South China share similarities with the orogenic type, but the nature of mineralization remains controversial, especially in terms of intracrustal versus subcrustal origin of ore fluids and metals and their relationships with the subduction of the Paleo-Pacific plate. This paper reports results of in situ analyses of minerals closely related to gold mineralization, including U-Pb ages of apatite and wolframite, and S-Pb isotopes of pyrite, from the Woxi Au-Sb-W deposit in the western Jiangnan Orogen, and use them to address the above problems.The Woxi deposit, which consists of several auriferous quartz lodes hosted by ductile–brittle shear zones in the Neoproterozoic slate. The hydrothermal mineralization and alteration processes are divided into four stages. Early-ore stage (S1) is characterized by disseminated, euhedral, porous, coarse auriferous pyrite (Py1) with minor amounts of arsenopyrite, siderite, and rutile in the bleached slate. Main-ore stage (S2) is characterized by subhedral to euhedral, auriferous pyrite (Py2) with compositional zoning, with small amounts of wolframite and apatite in quartz veinlets. Late-ore stage (S3) is represented by scheelite and stibnite with minor amounts of native gold and anhedral, dendritic auriferous pyrite (Py3) in quartz veinlets. Post-ore stage (S4) features a quartz-calcite-barite-chlorite mineral assemblage that occurs as veinlets or in pressure shadows of Py1.Apatite and wolframite associated with Py2 yield a consistent U-Pb age of ca. 141 Ma, which is corresponded to a time when the Paleo-Pacific plate started to roll back, and a Basin-and-Range style tectonic regime began to developing in South China. The different stages of pyrite have variable S isotopes, with the δ34SCDT values (mainly between −6‰ and +1 ‰) largely overlapping with those of the metasomatized mantle (−5‰ ∼ + 5 ‰), and Pb isotope ratios between crustal and mantle values. Taking these results together, we proposed that the Woxi deposit and many other gold deposits in the JOB formed from subcrustal processes involving the metasomatized upper mantle above the subduction zone. Given the extended distance from JOB to the Paleo-Pacific plate boundary, the metasomatized mantle underneath the JOB is likely initially formed during the plate subduction leading to the formation of the JOB during the Neoproterozoic, which is further fertilized by upwelling asthenosphere due to rollback of the Paleo-Pacific plate in the Mesozoic.

Gradient-tailored and heterointerface-rich architectures enable superior Li-ion storage performances of GeS2@NiS@N-doped carbon microspheres

The mesoporous compositional gradient nitrogen-doped carbon encapsulated germanium disulfide-nickel sulfide (abbreviated as “GeS2@NiS@NC”) microspheres have been synthesized. The Ni3Ge2O5(OH)4 microspheres precursor is firstly prepared by a hydrothermal mineralization process, which transforms to Ge3Ni5 microspheres by high temperature reduction. A thin polydopamine shell protects the microsphere architecture, which is converted into nitrogen-doped carbon layers. The GeS2@NiS@NC microspheres are finally fabricated via a high temperature interdiffusion vulcanization process induced by Kirkendall effect, during which the interdiffusion rate of Ni atoms is much faster than that of Ge atoms leading to the gradual composition changes from the exterior (NiS phase is rich) to the interior (GeS2 phase is rich) throughout a single microsphere. The GeS2@NiS@NC microspheres show unique structural advantage of the abundant heterogeneous interfaces, which accelerates the Li+ diffusion kinetics proved by density functional theory results. Besides, the in-situ XRD analyses reveal a continuous lithiation sequence as the compositional gradient from NiS to GeS2, during which the in-situ generated Ni clusters from NiS construct a continuous and penetrating e− transport channel throughout the microsphere. As a result, the GeS2@NiS@NC microspheres exhibit improved cycling stability and rate capability when employed as anodes for lithium ion batteries.

In situ apatite U-Pb dating for the ophiolite-hosted Nianzha orogenic gold deposit, Southern Tibet

Mineralization age dating is essential for understanding orogenic-type gold metallogeny, but suitable minerals for dating are not always available. Apatite can incorporate considerable amount of U and Th, making it a potential U-Pb geochronometer to study hydrothermal alteration and mineralization processes. The newly-discovered Nianzha is a large orogenic Au deposit (∼25 t @ 3.08 g/t Au) and located in the contact fault zone between ultramafic rocks and diorite in the Renbu tectonic mélange of southern Tibet. Two different types of apatite were identified in the Nianzha gold deposit: type I magmatic apatite hosted in diorite and syenite, and intergrown with other magmatic minerals; type II hydrothermal apatite hosted in mineralized diorite. These apatite grains are coarse euhedral granular and closely associated with auriferous sulfides (e.g., pyrite, chalcopyrite, galena). Type I apatite is F- and SO3-rich, whereas type II apatite is distinct from type I apatite by its significantly higher Cl, Mn, rare earth elements (REE), U, Th, and As contents, indicative of a hydrothermal origin. Thus, formation age of type II apatite reflects the timing of gold mineralization. Two type I magmatic apatite samples yielded similar discordia U-Pb ages of 80.35 ± 1.56 Ma (MSWD = 1.3; n = 86) and 79.53 ± 1.27 Ma (MSWD = 0.91; n = 72), respectively, whilst type II hydrothermal apatite yielded a discordia age of 44.60 ± 1.45 Ma (MSWD = 1.2; n = 64). The gold mineralization age is consistent with that of nearby orogenic gold deposits (e.g., Mayum, Bangbu, Zhemulang, and Juqu) in the region. Therefore, we suggest that hydrothermal apatite U-Pb dating can effectively constrain the timing of orogenic Au mineralization events.

Well-Constrained Mineralization Ages by Integrated 40Ar/39Ar and U-Pb Dating Techniques for the Xitian W-Sn Polymetallic Deposit, South China

Abstract Mineralization ages of many mineral deposit types (such as orogenic Au, stratabound Cu, and Mississippi Valley-type Pb-Zn deposits) are still difficult to date by the traditional isotopic chronometry because of the lack of suitable minerals. We have made efforts to establish a widely suitable dating technique to determine ore formation ages using a high-precision 40Ar/39Ar method on ubiquitously present fluid inclusions in quartz, sphalerite, and other nonpotassium minerals from hydrothermal deposits. The Xitian W-Sn polymetallic deposit in central South China contains several minerals suitable for isotopic dating for interchronometer comparison. 40Ar/39Ar laser step heating of 16 micas from ore veins, greisen, and metallogenic granites yields flat age spectra and thus well-defined ore formation ages ranging from 152.4 ± 1.5 (2σ) to 148.1 ± 1.4 Ma with an average of 150.2 ± 0.6 Ma. 40Ar/39Ar progressive crushing of nine quartz samples produces well-defined isochron lines for their primary fluid inclusions corresponding to isochron ages of 153.7–149.9 Ma with an average of 151.6 ± 0.6 Ma. Cassiterites from three hand specimens have weighted mean 206Pb/238U ages of 151.5 ± 1.7 (2σ), 149.7 ± 2.1, and 151.7 ± 2.1 Ma. All these new geochronological dates and previous molybdenite Re-Os ages yield well-constrained mineralization ages of 153–148 Ma for the Xitian W-Sn polymetallic deposit, which also confirms conclusively that the quartz 40Ar/39Ar progressive crushing technique is a feasible, valid dating technique. Furthermore, significant age information on the secondary fluid inclusions is potentially obtained simultaneously by this technique. We expect that this novel dating technique will be widely applied to determine the geologic fluids trapped in minerals during hydrothermal mineralization, hydrocarbon accumulation, metamorphism, tectonic activities, and other geologic processes.

Discovery of the large-scale Huangtian scheelite deposit and implications for the structural control of tungsten mineralization in southeastern Yunnan, south China

The large-scale Huangtian scheelite deposit represents one of the most important such deposits discovered recently in southeastern Yunnan, China. Results of the geological, metallotectonic, and geochemical investigations indicate that this deposit formed in a magmatic hydrothermal system during the Yanshanian period. Its deposition is controlled by the ore-hosted structure of a secondary fold and by interlayer faults (F0-1 and F0-2), which are linked to the ore-guided structure of a secondary oblique strike-slip fault (F7) associated to the regional Maguan deep fault, and to an EW-trending tectonic zone that represents the main metallogenic tectonic system. The oblique strike-slip structure and the Tianchong granitic porphyries, located along the southern margin of the Laojunshan granite body, are primary ore-controlling structures, which directly controlled the movement of the ore-bearing fluid and its subsequent precipitation within the Huangtian scheelite deposit. The distribution of the orebodies is controlled by a group of metallogenic structural surfaces: the fold and fault systems, as well as a silicon-calcium surface. Silicification, fluoritization, and calcitization are the main hydrothermal alterations observed and exhibited a distinct alteration zonation. The hydrothermal mineralization process can be divided into three stages: the quartz-fluorite-(scheelite-tourmaline) stage, the scheelite-quartz-calcite- (fluorite) stage, and the calcite-pyrite-quartz-scheelite stage. The evolution of the mineralizing fluid proceeded as follows: medium-temperature and low-salinity fluid → medium- to low-temperature and low-salinity fluid → low-temperature and low-salinity fluid. The results concerning oxygen and hydrogen isotopic compositions demonstrate that the ore-forming fluids derived from a magmatic fluid mixed with a small amount of meteoric water. Overall, these features indicate that the Huangtian scheelite deposit represents a medium- to low-temperature magmatic hydrothermal deposit that is obviously controlled by the EW-trending tectonic zone. This study demonstrates the significance of such mineral exploration in similar geological regions.

The use of pXRF for light element geochemical analysis: a review of hardware design limitations and an empirical investigation of air, vacuum, helium flush and detector window technologies

Light element data are required for robust and accurate lithogeochemical interpretations and are important components in the study of hydrothermal alteration and mineralization processes. In this contribution we review the latest available portable energy dispersive X-Ray Fluorescence (pXRF) technologies exclusively in the context of light element analysis, with focus on the acquisition of data for Na, Mg, Al and Si. We discuss pXRF hardware design limitations, quantify variables that attenuate X-ray energies through numerical modelling, including common pXRF configurations, and empirically investigate modern pXRF technologies used to mitigate X-ray attenuation and improve light element analysis. The void between the sample and detector is a key issue regarding the success of pXRF light element analysis. Dry-air (normal conditions), vacuum purge and helium flush systems are evaluated. Modelled data that use a nominal sample-detector void of 10 mm show that using helium in lieu of air improves X-ray transmission effectiveness from ≈2% to ≈99% for Na and ≈10% to ≈100% for Mg. Modelled detector window data show that using a graphene detector window in lieu of a traditional beryllium detector window improves X-ray transmission effectiveness for Na from ≈38% to ≈64% and ≈57% to ≈77% for Mg. Progressive X-ray transmission effectiveness equates to ≈63% Na and ≈76% Mg when using a helium-graphene pXRF configuration v. ≈1% for Na and ≈6% Mg when using a traditional in-air beryllium pXRF arrangement (i.e. without sample or X-ray entrance window media). Empirically determined improvements of the resolved signal are more modest than those of modelled X-ray transmission effectiveness data. Instrument noise, spectral overlaps and random counting errors are unavoidable and inherent with the limitations of modern detector technologies. However, the employment of helium with graphene detector window technology allows very precise data to be obtained at significantly shorter scan times (i.e. 20 s, instead of the traditional 60–180 s, i.e. 3–9 times faster): a scan time of 20 s can achieve a precision of ≈18% @ ≈0.4% Na and ≈8% @ ≈0.3% Mg for elemental interference-free samples. Precision will improve with increasing analyte concentration.

Physicochemical Modeling of Hydrothermal Mineralization Processes at Ni–Co–As (±U–Ag), Co–S–As (±Au–W), and Cu–Co–As (±Sb–Ag) Deposits

The paper reports generalized investigation data on the composition of metal-bearing fluids at hydrothermal cobalt deposits, which formed in different geodynamic settings during the development of alkali and alkali-basic intrusions and dikes. To determine the physicochemical parameters of ore deposition from fluid inclusions in minerals, both traditional and new instrumental thermobarogeochemical methods were used: thermometry, cryometry, and Raman spectroscopy; the concentrations of ore- and rock-forming elements in individual fluid inclusions were evaluated by LA-ICP-MS. The results served as the basis for a study focused on thermodynamic modeling of joint transport and deposition of Co, Ni, Cu, Fe, Mg, Ca, Ag, Au, Bi, U, Pt, and Pd; the number of equilibrium states of the hydrothermal system similar in composition to the natural ore-forming fluids was also calculated. The physicochemical factors of native Au, Ag, Pt, and Pd in the ores at such deposits were revealed. These data can be used to develop correct genetic models for the ore-forming systems of the cobalt deposits proper and to solve the problem of searching for them.

Age and genesis of polymetallic veins in the Freiberg district, Erzgebirge, Germany: constraints from radiogenic isotopes

The Freiberg mining district in the Erzgebirge hosts three principal types of polymetallic veins. These are (1) the quartz-bearing polymetallic sulfide type, (2) the carbonate-bearing polymetallic sulfide type, and (3) the barite-fluorite-sulfide type. We investigated the genesis of each vein-type using Rb-Sr sphalerite geochronology, Sm-Nd fluorite geochronology, and Pb, Sr, and Nd isotope systematics of ore and gangue minerals. Field relationships and the Rb-Sr and Pb isotope systematics of sulfides from quartz-bearing polymetallic sulfide veins and carbonate-bearing polymetallic sulfide veins confirm their close genetic affiliation and yield a combined Rb-Sr errorchron age of 276 ± 16 Ma. The high mean squared weighted deviation (MSWD) value of 42 on the regression is considered to reflect initial isotopic heterogeneity, which is probably related to fluid-rock interaction during the hydrothermal mineralization process. Although some sphalerites from barite-fluorite-sulfide veins have strongly disturbed Rb-Sr isotope systematics, six sphalerites and one co-genetic fahlore yield a robust isochron age of 121.3 ± 4.2 Ma with an MSWD of 2.9. This age is supported by a fluorite Sm-Nd isochron age of 101 ± 18 Ma (MSWD = 1.3). The new ages and radiogenic isotope data place robust constraints on the long-held hypothesis that veins in the Freiberg district formed during two hydrothermal events. The Lower Permian age of first stage quartz-bearing polymetallic sulfide veins and carbonate-bearing polymetallic sulfide veins coincides with post-Variscan crustal reorganization and Rotliegend volcanism. The Mid-Cretaceous age of second stage barite-fluorite-sulfide veins coincides with opening of the North Atlantic Ocean during the break-up of Pangea.

Hydroxyapatite and dittmarite precipitation from algae hydrolysate

Several research efforts across the globe have been concerned with addressing the technical barriers in the commercialization of algae-based sustainable biorefineries. Nutrients cost and management and in particular, phosphorus, have been highlighted as one of the most significant challenges in algae cultivation and downstream processing. In this study, 83wt% of phosphorus present in Scenedesmus sp. microalgae was extracted as water-soluble phosphate in aqueous phase via flash hydrolysis process while preserving the algae lipids. Subsequently, the phosphate containing aqueous phase (algae hydrolysate) was used for producing dittmarite and hydroxyapatite by two different mineralization processes. In the first pathway, more than 97wt% of the phosphate in the hydrolysate was recovered in the form of carbonate-hydroxyapatite, a valuable biomaterial, at 280°C within one hour of residence time via hydrothermal mineralization process. Whitlockite as the secondary phase was also observed along with the hydroxyapatite. In the second pathway, 67wt% of the phosphate and 6wt% of nitrogen were recovered as dittmarite (magnesium ammonium phosphate), an effective slow-release fertilizer, at 20°C via an atmospheric precipitation process. The effects of seeding, temperature, reaction time, and mineralizers to PO4 molar ratio on phosphate removal as well as product yield were studied. This is the first kind of study in which flash hydrolysis and mineralization processes were integrated to provide an energy efficient platform for phosphorus recovery from microalgae in forms of value added compounds that could be suitable for long-term storage and handling. Through this experimental study, we report the shortest residence time for hydroxyapatite precipitation from an algal hydrolysate. The short residence could substantially save in reactor size and processing time as well as provide an option for high throughput which could result in a significant cost reduction in algae to bioproducts and biofuels.

Effect of Reaction Time on Phosphate Mineralization from Microalgae Hydrolysate

The development of algal biorefineries is strongly associated with the nutrient management, particularly phosphorus, which is a limited mineral resource. Flash hydrolysis (FH) has been widely applied to a variety of algae species to fractionate its constituents. This chemical-free, subcritical water technique was used to extract more than 80 wt % of phosphorus available in the Scenedesmus sp. as water-soluble phosphates in the aqueous phase (hydrolysate). The phosphate-rich hydrolysate was subjected to the hydrothermal mineralization (HTM) process at 280 °C and 5–90 min of residence time to mineralize phosphates as allotropes of calcium phosphate such as hydroxyapatite (HAp) and whitlockite (WH). In the current study, the effect of reaction time on phosphate mineralization from the hydrolysate as well as the composition, structure and the morphology of the precipitates were studied. Calcium hydroxide and commercial HAp were used as the mineralizer and seeding material, respectively. More than 97 wt % of p...

Magnetite geochemistry of the Heijianshan Fe–Cu (–Au) deposit in Eastern Tianshan: Metallogenic implications for submarine volcanic-hosted Fe–Cu deposits in NW China

The Heijianshan Fe–Cu (−Au) deposit is located in the Aqishan–Yamansu belt in Eastern Tianshan, NW China. As a typical Fe–Cu deposit in the region, Heijianshan is hosted in the Upper Carboniferous Matoutan Formation submarine volcanic/volcaniclastic rocks. Alteration styles, mineral assemblages and vein crosscutting relationships divide the hydrothermal alteration and mineralization processes into seven stages, namely the chromite (Stage I), epidote (Stage II), magnetite (Stage III), pyrite (Stage IV), Cu (–Au) (Stage V), late veins (Stage VI) and supergene (Stage VII) alteration/mineralization stages. Magnetite mineralization comprises the hematite (Stage III–A) and main magnetite (Stage III–B) mineralization sub-stages.The Heijianshan magnetite ores consist of massive (with mushketovite (MOM) or sulfides (MOS)), disseminated (DO) and magnetite clasts (with chromite (MWC) or without chromite (MNC)) ores. Magnetite in massive- and disseminated ores is featured by (1) depletion in Zr, Nb and Ta; (2) low Ti (<2wt.%) and Al (<1wt.%); and (3) Ni/Cr≥1, which all reflect a hydrothermal origin. Moreover, magnetite in massive- and disseminated ores has lower Cr (MOM: 0–13.2ppm; MOS: 0–12.9ppm; DO: 3.57–133ppm) than magnetite clasts ores (MNC: 849–2544ppm; MWC: 835–44,132ppm). However, the high Cr in the magnetite clasts ores may have been inherited from the chromite they replaced. From the magnetite clasts to disseminated/massive ores, formation temperature decreased and fO2 increased, which may represent the major controls on the formation of the various magnetite ore types. Compositions of the ore fluids and host rocks, formation of coexisting minerals and other physicochemical parameters (such as T and fO2) may have variably influenced the magnetite geochemistry in the different Heijianshan ore types, with fluid compositions probably playing the most important role.Discrimination diagrams, for instance, Cr vs. Co/Ni, Cr vs. Ti, V vs. Cr and Ni vs. Cr, may be useful for magnetite mineralization type differentiation in other submarine volcanic-hosted Fe/Fe–Cu deposits in the Aqishan–Yamansu belt. Geochemical discrimination diagrams, alteration and mineralization paragenesis indicate that the Heijianshan Fe–Cu (–Au) deposit is best classified as an IOCG-like deposit, which offers a new insight for classifying and characterizing ore genetic types for similar Fe and Fe–Cu deposits in Eastern Tianshan.

Geology, geochemistry and tectonic settings of the molybdenum deposits in South China: A review

South China Block (SCB) is the area including the Yangtze Craton and the Huanan Orogen where scattered Precambrian terranes are usually regarded as segments of Cathaysia Land. It is the third most important molybdenum metallogenic province in China, next to the Qinling-Dabie area and Northeast China, containing 29 Mo-only or Mo-dominated, 9W-Mo(-Sn-Bi) and 8 Cu-Mo deposits. These 46 deposits are located mainly in: (1) the Lower Yangtze River Belt of the northeastern Yangtze Craton, (2) the Northern Jiangnan Orogenic Belt that is generally considered a Meso-Neoproterozoic magmatic arc complex accreted onto the southeastern margin of the Yangtze Craton, (3) the Wuyi-Yunkai Orogenic Belt characterized by local exposures of Proterozoic metamorphic terranes and the more widespread Sinian (Uppermost Proterozoic) to Triassic sedimentary sequences, and (4) the Southeast Coastal Volcanic Belt characterized by Yanshanian andesitic to felsic volcanic rocks. Their genetic types are dominated by porphyry and skarn mineral systems, with only a few quartz-vein systems. The orebodies form veins, lens, cylindrical shapes, pipes, or irregular in shape, usually controlled by faults at various scales and volcanic-subvolcanic complexes. The host-rocks are variable in lithologies, including granites, porphyries, volcanic breccias and tuffs, clastic sediments and carbonate rocks, but the high-grade orebodies are usually hosted in carbonate-shale sequences. Hydrothermal mineralization processes can be generally divided into four stages, from early to late, they are (1) K-feldspar-quartz veins or veinlets, (2) quartz-molybdenite stockworks, (3) quartz-polymetallic sulfide stockworks, and (4) quartz-carbonate-fluorite veinlets. Fluid-rock interaction as exemplified by wallrock alteration evolved from K-silicate alteration (K-feldspar-quartz-mica), through phyllic (quartz-sericite-chlorite-epidote), to propylitic or argillic alteration, with skarn alteration typically occurring in skarn-type mineral systems. Hydrothermal mineral assemblages vary between two end-members, namely the dry system formed by CO2-rich fluids and marked by quartz, K-feldspar, fluorite, carbonate and epidote, and the wet system mainly originated from CO2-poor fluids and composed of biotite, sericite and chlorite. The ore-forming fluids are magmatic in origin and show high-temperature and high-salinity. The melt-fluid systems forming Cu-Mo deposits are more oxidizing than those forming the W-Mo or Mo deposits, as suggested by accessory minerals in granitoids and daughter minerals in fluid inclusions. The Cu-Mo deposits are related to the I-type granitic rocks (adakite-like), whereas the W-Mo and Mo-only systems are related to granitic rocks of S- or A-types, although all of them show high K contents. Available isotope ages show that the Mo and Mo-bearing deposits were predominantly formed in the early Yanshanian Orogeny (170–134Ma), followed by the late Yanshanian Orogeny (110–92Ma) and the Caledonian Orogeny (450–410Ma). The Caledonian Mo-mineralization has been observed only in the Wuyi-Yunkai Orogenic Belt and related to the collision between the Yangtze Craton and the pre-Devonian Huanan Orogen or terranes separated from the Cathaysia Land, linked to the assembly of the Gondwana supercontinent. The Early Yanshanian mineralization affected the entire Huanan Orogen and the eastern Yangtze Craton, and resulted from the syn- to post-collisional tectonism following the closure of eastern Paleo-Tethys. The Late Yanshanian Mo deposits mainly occur in the Southeast Coastal Volcanic Belt and the southeastern margin of the Wuyi-Yunkai Orogenic Belt, and are related to the westward subduction of the Paleo-Pacific plate. The skarn-type mineral systems generally show lower Re contents than the porphyry-type deposits in a same tectonic unit, suggesting that carbonate host-rocks have lower Re contents than the causative porphyries. The Re contents in molybdenites from porphyry or porphyry-skarn Cu-Mo systems are >50ppm, mainly >100ppm, suggesting a source significantly contributed by the mantle; whereas the Re contents in molybdenites from the Mo-only or W-Mo-dominated deposits are <100pm, mainly <50ppm, indicating a genetic relation to the crust-sourced granitic magmatism.

OKYANUS ORTASI SIRTLARDA OLUŞAN MASİF SÜLFİD YATAKLARININ SIRLARI VE KÜRE- MAĞARADORUK BAKIR YATAĞI

Kure region is located in western part of the Pontide tectonic belt. The oldest rocks around Kure are Paleozoic metamorphic rocks constituting “Rhodope-Pontide” continent. Liassic-pre Liassic ophiolites and basaltic volcanics, which form Paleotethys Ocean Floor are situated on “Rhodope-Pontide” continent as Paleotethys Ocean Floor residuals. Massive sulfide deposits in Kure Region are closely associated with pre Liassic – Liassic basaltic volcanics and intercalating black shale. These deposits are considered to have formed during hydrothermal mineralization processes when basaltic volcanism had stopped and defined as “Black Smoker” today. Massive sulfide bodies in Magaradoruk copper deposits are lens shaped. Although ore lenses take place sometimes in basalts and black shales, they are generally located on basalts and are covered by black shales. In Kure region, fold structures are intensely observed, and Magaradoruk deposit is located on western flank of an overturned anticline. Magaradoruk deposit is formed by several small and a big ore body and by less developed, underlying stockwork disseminated ore. The big ore body is 600 m long, 250 m wide and nearly 40 m thick. As main ore minerals; pyrite and chalcopyrite are observed. In few amounts; marcasite, magnetite, hematite, sphalerite, covelline, neo-digenite, malachite, azurite, fahlers are seen. In fewer amounts; bravoite, lineiite (karolite), limonite, and in trace amounts; chromite, rutile anatase, chalcosine, cuprite, tenorite, pyrrhotite, valleriite, bornite, galenite, native copper and native gold are observed. Main gangue minerals are; quartz, siderite-ankerite calcite, dolomite and chlorite. Magaradoruk massive sulfide deposit within basaltic rocks resembles to Siirt Madenkoy, Ergani massive sulfide deposits, to “Cyprus” type massive sulfide deposits and modern Cyprus type massive sulfide deposits in terms of mineral contents; and to Ergani Mihrapdagi, Papuke, Pakotai and Parakoa deposits in terms of cover rocks, which are Cyprus type massive sulfide deposits, in New Zealand

Characteristics of Breccias and C‐O‐Sr‐S Isotope Geochemistry of the Duocaima Pb‐Zn Deposit in Tuotuohe, Qinghai Province: Implications for the Ore‐forming Process

AbstractThe Duocaima carbonate‐hosted Pb‐Zn deposit is a newly found large deposit in the southern area of Qinghai Province. In this paper, the characteristics, genesis, significance to Pb‐Zn mineralization of the widely developed breccias, and the ore‐forming process have been carefully studied based on geological documentation of drilling holes, microscopic observations of petrography and microstructure and some stable isotope measurements. Based on the compositions of the clast and matrix, the breccias can be classified into three types: limestone clasts cemented by marl; limestone clasts with fine‐grained calcareous materials; and limestone clasts cemented by hydrothermal calcite. The mineralization in the first type of breccia is weak, whereas it is strong in the latter two types of breccias. According to the locations of occurrence and structural characteristics of the breccias along with the relationship between the breccias and mineralization, part of the limestone clasts that are cemented by marl and outcrop in the contact zone between the Wudaoliang Formation (Nw) and the underlying Jiushidaoban Formation (Pj) are attributed to synsedimentary fault‐genetic breccia, whereas the last of the limestone clasts that are cemented by marl and developed in the Jiushidaoban Formation (Pj) are attributed to the breccia generated by karst cave collapse; the limestone clasts with fine‐grained calcareous materials and the limestone clasts cemented by hydrothermal calcite are attributed to breccia formed by hydrothermal dissolution. The breccia formed by karst collapse had consistently evolved for a long period of time, while the breccias with other origins were formed around the period of mineralization (i.e., about or slightly later than 20–16 Ma). The breccia generated by karst cave collapse and hydrothermal dissolution are somewhat related; the formation of the breccia from karst cave collapse provided open space for the later mineralization and reaction between hydrothermal fluids and host rocks, and the subsequent strong dissolution by hydrothermal fluids transformed some of the breccia formed earlier by karst cave collapse. Meanwhile, carbonate host rocks with breccias and brecciaed mineralization can be a potential sign of Mississippi Valley Type (MVT) deposits and important indicators for regional mineral exploration. The δ13CV‐PDB, δ18OV‐SMOW, and 87Sr/86Sr values of hydrothermal calcite in the Duocaima deposit range from 4.3‰ to 7.1‰, 14.9‰ to 20.1‰, and 0.707494 to 0.708185, respectively; the δ13CV‐PDB, δ18OV‐SMOW, and 87Sr/86Sr values of the host limestones of the Jiushidaoban Formation range from 3.6‰ to 5.3‰, 18.0‰ to 20.5‰, and 0.707372 to 0.707945, respectively. The δ13CV‐PDB and 87Sr/86Sr values of hydrothermal calcite and limestone are similar, indicating single sources of C and Sr in this deposit, with the likely source being the limestone of the Jiushidaoban Formation. The minor scattering of the δ18OV‐SMOW values suggests that different O isotope fluids underwent the isotope exchange reaction. The C‐O‐Sr isotope characteristics indicate that the host limestones experienced a dissolution and precipitation process during mineralization, which is beneficial to improving the porosity of host rocks and promoting the precipitation of metal sulfides. The δ34SV‐CDT value of the breccia‐type mineralization sulfides ranges from −30.4‰ to −0.3‰; that is, the δ34SV‐CDT value is negative with considerable variation, illustrating that during the breccia‐type mineralization process, the bacteriogenic reduction of sulfates provided the vast majority of sulfur, whereas the thermochemical reduction of sulfates was relatively unimportant The brecciation that occurred as a result of karst cave collapse was mainly generated by the dissolution of groundwater; however, the brecciation related to hydrothermal dissolution and mineralization processes were caused by mixing of different fluids.