Cathodoluminescence Textures Research Articles

Cathodoluminescence textures and trace elements in quartz: Constraints on Ag mineralization in adularia–sericite epithermal systems

Cathodoluminescence textures and trace elements in quartz: Constraints on Ag mineralization in adularia–sericite epithermal systems

Fluid overprints and mineralization of the Zhuguangshan granite-related U district in China: Recorded by cathodoluminescence textures and chemistry of quartz

Most high-grade U ores are mined from quartz veins hosted in granites. The veins formed at shallow depths during episodic hydrothermal activity, however, the evolution of multiple stage fluids is not well constrained. In this study, we collected 56 quartz samples from the world-class, granite-related, Zhuguangshan U district (>17,000 t U from seven deposits) in southern China. Their textures and compositions were analyzed using scanning electron microscope cathodoluminescence (SEM-CL, n = 98) and laser ablation-induction coupled plasma-mass spectrometry (LA–ICP–MS, n = 643). Four types of quartz were identified, including magmatic quartz, early hydrothermal euhedral quartz, ore stage hydrothermal quartz (U-rich), and late hydrothermal quartz. New quartz textures and chemical compositions show that the transition of early hydrothermal quartz from the magmatic to hydrothermal stages is discontinuous, unlike the continuous trend observed in most magmatic-hydrothermal systems. Ore stage quartz is CL dark (with a peak at 650 nm), occurs as rims on early barren quartz, and has high contents of Mn, Al, and Sb. Altered textures of magmatic quartz developed through fluid-rock reactions at low temperatures, while rimmed textures of hydrothermal quartz formed during subsequent late-stage U-bearing fluid events, which played a crucial role in U mineralization. Quartz in the Zhuguangshan U district has distinct features compared to other magmatic-hydrothermal systems that can guide exploration for high-grade ore in this, and perhaps other, granite-related U systems.

Quartz fluid inclusions and trace elements in the Lailisigaoer porphyry Mo deposit, Western Tianshan, Xinjiang: Fluid evolution and metallogenic mechanism in magmatic-hydrothermal system

The Lailisigaoer deposit is a typical porphyry Mo deposit located in the late Paleozoic Boluokenu metallogenic belt of Western Tianshan, NW China. This study aims to understand molybdenum mineralization and the dynamics of magmatic-hydrothermal fluid within the porphyry system, focusing on fluid inclusion, cathodoluminescence textures, and trace elemental composition in various generations of quartz. Six vein types in the Lailisigaoer deposit are classified as comb quartz veins with unidirectional solidification texture (UST, QI), actinolite/biotite ± quartz veinlets (M-type, QII), quartz-chalcopyrite vein (A-type, QIII), quartz-molybdenite vein (B-type, QIV), quartz-pyrite vein (D-type, QV) and quartz-carbonate vein (E-type, QVI). Micro thermometry data indicate decreasing homogenization temperatures in primary fluid inclusions from UST to E-type veins. The magmatic-hydrothermal fluids associated with UST and M-, A-, B-, D-, E-type veins underwent a transition from high temperature (342–495℃), high-pressure (∼1.25 kb), and variable salinity (6.7–41.1 wt%NaCl) in the H2O-CO2-NaCl system to low-temperature (142–238℃), low-pressure (∼0.25 kb), and low-salinity (1.6–5.1 wt%NaCl) in the H2O-NaCl system. This evolution is reflected in the proportion of quartz with oscillatory zones decreasing and irregular quartz increasing, indicating a shift from turbulent to stable fluid conditions. Furthermore, a gradual reduction in Ti concentration (from 79 ppm in UST to 1.4 ppm in E-type quartz) suggests a decrease in fluid temperature during the magmatic-hydrothermal evolution. Mineralization primarily occurs in A- and B-type veins, with molybdenum precipitation attributed to fluid immiscibility in a medium–high temperature (240–368 ℃) and high pressure (∼0.95 kb) environment. The A-type veins (mean 31 ppm in Ti concentrations) consist of equigranular (dark-core) (QIII-1) and patchy inhomogeneous CL-gray quartz (QIII-2). The B-type veins (mean 24 ppm in Ti concentrations) are characterized by equigranular (bright-core) inhomogeneous quartz (QIV-1) with growth zones that are cemented by later mosaic homogeneous CL-gray quartz (QIV-2). Based on the quartz-Ti thermometer, the mineralized veins (A- and B-type) were confined to be formed at depths of 2.8–3.6 km, with molybdenum mineralization occurring at 3.4–3.6 km. Molybdenum mineralization initiates during the QIV-1 crystallization period in magmatic-hydrothermal fluids and terminates in the QV-2 generation.

Scheelite composition fingerprints pulsed flow of magmatic fluid in the Fujiashan W skarn deposit, eastern China

Abstract Scheelite (CaWO4) is an economically important W mineral in skarns that form when magmatic fluids exsolved from a granitic intrusion react with carbonate wall rocks. In the Fujiashan W skarn deposit, scheelite formed during four stages of the hydrothermal skarn development. We present cathodoluminescence (CL) images and in situ trace element and Sr-O isotope data of scheelite from these four stages, i.e., scheelite in prograde and retrograde skarn, quartz-sulfide veins, and late calcite replacements. Scheelite from prograde skarn and quartz sulfide veins are homogeneous and show oscillatory zoning textures in CL images, whereas scheelite from retrograde skarn and late carbonate stages display dissolution-reprecipitation and patchy textures. The brightness of CL textures decreases with a higher substitution of Mo. Molybdenum-rich scheelite (up to 2.1 wt%) is characterized by relatively high contents of Nb and Ta (up to 156 and 0.9 ppm, respectively), positive Eu anomalies, high-δ18O values (5.2 to 5.9‰), and relatively low-87Sr/86Sr values (0.70661 to 0.70727), and has grown in a system with a continuous supply of magmatic fluid. Molybdenum-poor scheelite (0.2 wt%) has low contents of Nb and Ta, negative Eu anomalies, low-δ18O values (4.2 to 4.3‰), and relatively high-87Sr/86Sr ratios (0.70748 to 0.70804). This type of scheelite formed in a system with a restricted flow of magmatic fluid during scheelite precipitation became increasingly depleted in elements that substitute into scheelite. The continued reaction of the magmatic fluid with the wall rocks and the precipitation of minerals from the fluid resulted in a systematic change of the δ18O and 87Sr/86Sr ratios. Chemical and isotopic variations in scheelite may reflect the pulsed flow of a magmatic fluid and do not require the involvement of different fluids or contrasting redox conditions.

Magmatic to hydrothermal evolution of the Gaogangshan Mo deposit, NE China: Mineralogical insights from quartz

Integrated study on cathodoluminescence (CL) textures and compositions of quartz is proven to be an effective way to reconstruct the ore-forming conditions and processes of porphyry system under subduction tectonic setting. However, little relevant research has been conducted on collision-type porphyry deposits. The Gaogangshan deposit in the northern Lesser Xing'an Range, NE China, consists of typical collision-type porphyry Mo mineralization related to Permo-Triassic granitic intrusions. Ore-forming process is recorded by multiple generations of quartz, including pre-ore stage quartz with unidirectional solidification texture (UST), early ore-stage quartz-molybdenite veins with K-feldspar alteration halos (Q1), late ore-stage quartz-sulfides veins with sericite alteration (Q2), and post-ore stage quartz veins (Q3) associated with calcite and fluorite. Cathodoluminescent textures, trace elements and fluid inclusions in quartz reveal physicochemical conditions, evolution of ore fluids and the Mo mineralization process. The UST quartz and Q1 veins are dominated by CL-bright homogenous and/or granular mosaic textures, containing more Ti concentrations (average = 35–42 ppm) than Q2 and Q3 veins. The molybdenite-bearing Q2 veins are dominated by CL-gray granular and zonal textures, displaying less CL intensity and lower Ti concentrations (average = 16 ppm) than early-stage quartz. The Q3 veins have the lowest CL-intensity and the lowest Ti concentrations (average = 2.5 ppm) among all quartz types. Three types of inclusions are identified in above quartz samples, including liquid–vapor aqueous inclusions, CO2-bearing liquid–vapor aqueous inclusions and halite-bearing multiphase aqueous inclusions. The ore-forming fluids in ore-stage Q1 and Q2 veins are dominated by large salinity variation (2.3–38.9 wt% NaCl equiv.), CO2-bearing (4.2–8.9 mol%) two-phase aqueous inclusions with vapor volumetric proportions of 30–65%. Intersections of fluid inclusion isochores with Ti-in-quartz isopleths yield quartz formation conditions of ∼2.2 kbar at ∼640℃ for UST quartz, ∼1.25 kbar at ∼510℃ for Q1, ∼1.0 kbar at ∼440℃ for Q2, and ∼0.37 kbar at ∼220℃ for Q3. The Gaogangshan porphyry Mo deposit formed at depths of 3.8 to 4.7 km.

Genesis of the Mianhuakeng granite-related uranium deposit, South China: Insights from cathodoluminescence imaging, fluid inclusions, and trace elements composition of hydrothermal quartz

The Mianhuakeng deposit is the largest granite-related U deposit in China, with multiple hydrothermal quartz veins. However, its genesis and ore-forming processes are still under discussion. In the present study, we have attempted to unveil the characteristics of ore-forming fluids and the metallogenesis of Mianhuakeng deposit with the help of cathodoluminescence (CL) imaging, fluid inclusions (FIs), trace elements, as well as hydrogen-oxygen (H-O) isotope compositions of hydrothermal quartz associated with U mineralization. Based on the crystallography and CL textures, four generations of hydrothermal quartz have been identified: early stage QtzⅠ quartz, main stage QtzⅡa and QtzⅡb quartzes, and late stage QtzIII quartz. QtzⅠ was formed by a continuous fluid flow in an open fluid system. The formation of QtzIIa was associated with a brief period of fluid flow in a compressive fluid system, whereas QtzIIb crystallized in an open system with a stable fluid flow. QtzIII was produced by fluid chemical fluctuation in an open system. These quartzes show high Al, variable Li, Na, K, and Ca, moderate Rb and Ba, and low Ti, Fe, Ge, and U contents. Al3+ and Ge4+ were incorporated into the quartz crystal lattice by substituting Si4+, helped by the change compensators composed of Li, Na, K, Rb, Ca, and Ba. The FIs microthermometry results suggested that ore-forming fluids were NaCl–H2O ± CO2 system with moderate to low temperatures and salinities. A gradually decreasing trend has been recorded for temperatures from 225 to 353 °C, through 153–302 °C, and toward 105–161 °C, respectively, with salinities changing from 6.0 to 10.1 wt% NaCl equiv, through 0.6–10.1 wt% NaCl equiv, to 0.5–5.7 wt% NaCl equiv from early to late stages. The H-O isotopic results indicated that the ore-forming fluids were originated from a mixture of deep magmatic and meteoric waters, with an increase in the amount of meteoric water from early to late stages. Fluid decompression and immiscibility were triggered by episodic fracturing of NS-trending fractures, which resulted in a fluid flow transition from extrusion to opening and the breakdown of uranyl complexes. The Fe2+ from altered granites reduced free U6+ to U4+, forming pitchblende (UO2) in hydrothermal quartz veins. Therefore, the Mianhuakeng deposit is thought to be of polygenic in origin and is controlled by several geological factors such as fracturing, fluid immiscibility, and redox reaction.

In Situ Trace Elements in Quartz and K-Feldspar from Felsic Igneous Rocks: A Titanium-in-K-Feldspar Geothermometer for Natural Magmatic Systems

Abstract Scanning electron microscope, cathodoluminescence (CL) imaging and laser ablation–inductively coupled plasma–mass spectrometry analyses were conducted on coexisting pairs of quartz and K-feldspar from 14 samples of various types of felsic igneous rocks. Difference of the concentration of trace elements in quartz and K-feldspar among plutonic, pegmatitic and volcanic rocks is closely related to the rock-forming process and P–T condition. In general, a decreasing Ti concentration and increasing Al, Li, and Ge concentrations from plutonic to pegmatitic quartz suggest a higher degree of magmatic fractionation and lower crystallization temperature. Sensitive elements to magma differentiation in K-feldspar such as Ba, Sr, and LREE show a decreasing trend from various granitic rocks to pegmatite, while Rb, Cs, Li, Ge, and P exhibit increasing trends. The K-feldspar from various types of felsic igneous rocks typically shows similar CL textures but relatively higher luminescence intensity compared with coexisting quartz. Both quartz and K-feldspar phenocrysts in the volcanic rhyolite have a bright rim and a dark core in CL images, corresponding to bimodal Ti concentrations. Among all samples, Ti concentrations in both quartz and coexisting K-feldspar positively correlate with their CL intensities, suggesting the activation of Ti-impurity in these minerals leads to increased CL intensity. Meanwhile, there is a good positive correlation between Ti concentrations in quartz and those in K-feldspar with an R2 value of 0.86. It is considered that Ti concentrations in the both minerals are mainly temperature dependent at relatively constant pressure on basis of a fair aTiO2 restriction. Here, for the first time, we calculated a titanium-in-K-feldspar (TitaniKfs) thermometer in the form of log (XTi, kfs/aTiO2) = −(3430 ± 268)/T(K) + (5.081 ± 0.298) for natural felsic magma systems. The Ti contents of K-feldspar (in ppm by weight) increase exponentially with reciprocal T at temperatures ranging from 500°C to 800°C, at 200–300 MPa. An application of this thermometer to granitic rocks from Xinjiang and Inner Mongolia in China fits well with other geothermometers. In addition, the present TitaniKfs thermometer is expected to be particularly useful in determining the temperature condition of K-feldspar-bearing extraterrestrial materials such as lunar rocks.

Trace elements and textures of scheelite in porphyry-skarn Cu-Au systems: The example of Dongguashan deposit, eastern China

Porphyry-skarn deposits are the major sources of Cu and Au in eastern China, and W is a common byproduct of these mines. Scheelite is the W-bearing mineral in these deposits, and is widespread in both porphyry and skarn ore, however, systematic variations in the textures and geochemistry of the scheelite are not well constrained. Here, multiple generations of scheelite in Dongguashan deposit provide an opportunity for systematic study of the evolution of scheelite textures and chemistry, and their implications for ore-forming processes in a porphyry-skarn Cu-Au system. Scheelite is widespread in the porphyry and skarn zones at Dongguashan, and five types of scheelite are identified. Type1 scheelite occurs in quartz-sulfide veins from the porphyry potassic alteration stage; it displays oscillatory zoning and patchy cathodoluminescent (CL) zones. Type2 and 3 scheelite show relatively homogeneous CL image and occur interstitial to garnet and pyroxene. Type4 scheelite from the skarn ore has patchy CL zones; type5 scheelite shows patchy (core-rim) CL texture and occurs in quartz-sulfide veins that cut massive skarn or skarn sulfide ore. We conclude that the oscillatory banding of type1 scheelite was controlled by crystal kinetics, whereas the patchy, chaotic and sector CL textures in other types were mainly produced by extrinsic fluids of variable composition. The trace elements Mo, Na, Nb, V and REE strongly affect the CL intensity of scheelite at Dongguashan, and trace elements Na, Nb, V and ∑REE decrease in the order type1 and 5 → type4 → type2 and 3. All scheelite types show Y/Ho ratios (12.5–30) similar to igneous rocks (20–27.5), indicating the tungsten mineralization is genetically related to the associated quartz monzodiorite. High Mo, Nb, V and the negative Eu anomaly in type1 scheelite indicate that the fluid related to the porphyry ore was oxidized and F-rich. The homogeneous compositions of type2, 3 and 4 scheelite, together with their weakly negative Eu anomalies show that they formed in a stable high T oxidized environment. The hydrothermal vein features with enrichment of REE (1 wt%) in the late type5 scheelite indicate it formed by injection of a late magmatic-hydrothermal pulse, and the variations in Eu anomalies in type5 suggest the fO2 gradually decreased in late fluids. Our study highlights that scheelite CL textures and geochemistry are effective for tracing multiple ore-forming processes in porphyry-skarn Cu-Au systems.

Cassiterite U–Pb, mica 40Ar–39Ar dating and cassiterite trace-element composition of the Furong tin deposit in the Nanling Range, South China

The Furong tin deposit (530,000 t Sn @ 0.8% Sn) is located in the southern part of the Mid–Late Jurassic, multiphase, granitic Qitianling batholith in the Nanling Range, South China. The spectrum of tin mineralization comprises skarn, chloritized granite, greisen, and quartz vein types, of which the skarn type is the most important. Cassiterite U–Pb dating provided Tera-Wasserburg lower intercept ages of 157.1 ± 1.5 Ma and 156.3 ± 1.5 Ma for skarn-type mineralization, 158.1 ± 1.4 Ma and 158.7 ± 1.6 Ma for chloritized granite-type mineralization, 155.8 ± 3.4 Ma for greisen-type mineralization, and 160.1 ± 1.7 Ma for quartz vein-type mineralization. These ages overlap with each other and define a pooled weighted mean age of 157.9 ± 1.1 Ma (2σ) for the tin ore system. Hydrothermal phlogopite from tin skarn and muscovite from tin greisen yielded younger 40Ar–39Ar plateau ages of 154.3 ± 1.9 Ma and 150.0 ± 1.5 Ma, respectively, which may reflect resetting due to post-ore fluid circulation. Distinctive cathodoluminescence textures and trace-element patterns of various cassiterite types indicate that the four ore types resulted from pulsed ore-forming fluids and changes in temperature in a single magmatic-hydrothermal system. In combination with the geological characteristics, the geochronological and trace-elemental data of cassiterite indicate that the formation of different ore types at Furong was associated with the most fractionated and latest alkali-feldspar granite of the Qitianling batholith, and resulted from the specific interactions of the ore-forming fluids with their granite and limestone host rocks.

Zircon U–Pb ages in El Chaltén Jurassic rhyolites (Chon Aike Silicic LIP, Argentina) reveal xenocrystic remnants of an unexposed lower basement of the Paleo-Pacific Gondwana margin

We investigate the Jurassic volcanic rocks of the El Quemado Complex in the El Chaltén region (Argentina), which correlate with the youngest eruptive event of the Chon Aike Silicic LIP in southern Patagonia. New zircon crystallization ages of the various silicic units were obtained using U–Pb geochronology measured by in-situ Laser Ablation Inductively Coupled Plasma Mass Spectrometry. The average ages for 12 samples range from 147 to 152 Ma. Xenocrystic zircon cores of Jurassic igneous zircons are characterized by complex cathodoluminescent textures wherein growth surfaces are truncated by dissolution surfaces that are in turn overgrown by euhedral growth zones that exhibit oscillatory magmatic zoning. The cores have a wide range of ages, from 185 Ma to 1.3 Ga. We combine our analyzed xenocryst zircon ages preserved in the El Quemado Complex rhyolites with a compilation of published xenocryst zircon ages documented from Cenozoic to Paleozoic volcanic and plutonic rocks throughout southern Patagonia. The combined datasets suggests three prominent geologic features not currently exposed on the present day surface: (1) widespread abundant Triassic through Permian (200–300 Ma) xenocrystic ages throughout the present day Andean region, which connect to current exposures in Northern Patagonian and that of the Antarctic Peninsula, marking the Paleo-Pacific Gondwanan margin, (2) the existence of widespread Early-Middle Ordovician to Cambrian ages throughout southern Patagonia, and (3) the presence of an old (∼1.0 Ga) crust below that of the Deseado Massif and Tierra del Fuego, which likely extends beneath the present-day Andes.

Cathodoluminescent textures and trace element signatures of hydrothermal quartz from the granite-related No. 302 uranium deposit, South China: A reconnaissance study for their genetic significances

Cathodoluminescent (CL) texture and trace element signature of quartz from granite-related uranium deposit in southern China has been investigated to discuss their genetic significance. Results show that the pre-ore quartz (Q1) generally has dark and homogeneous (or slightly mottled) luminescent texture that may result from annealing of original CL textures; the syn-ore quartz (Q2) generally shows bright and oscillatory luminescent texture and the post-ore quartz (Q3) displays bright and homogeneous luminescence texture. LA-ICPMS analyses suggest Al, Li, K, Na and Ca are the most abundant elements in various generations of quartz and mainly occur as solid solution within the crystal lattice, in which Al can be incorporated into quartz by substituting Si in the crystal lattice, with additional cations (e.g., K, Na, Li and Ca) to keep the charge balance. The negative correlation between Ge and Al suggests that Ge may substitute Si independently due to the similar ion radius and charge. Fe and U may be incorporated into quartz in the form of micro-inclusions. The homogeneous CL texture and low concentration of trace elements indicate that the Q3 likely precipitated under stable thermodynamic conditions.The low Ti concentration and oscillatory euhedral growth zones of CL textures suggest that syn-ore quartz (Q2) may have precipitated from a low-temperature hydrothermal fluid. Thus, it can be inferred that the ore-forming fluid in the No. 302 uranium deposit could be of a low-temperature hydrothermal fluid from which the quartz-pitchblende vein precipitated from, which is also supported by the results from fluid inclusion studies. The significantly large variations of Al and other trace elements concentrations in the syn-ore quartz were likely indicative of the large fluctuations of pH values of ore-forming fluid, probably resulting from the CO2 effervescence or phase separation from ore-forming fluid, which further led to decomposing of uranyl carbonate complexes (UO2(CO3)2−), and finally caused the uranium minerals depositing in the favorable structural traps to form the No. 302 uranium deposit. This study highlights that CL textures and trace element chemistry of quartz related to mineralization can be used to fingerprint the physical and chemical history of ore deposit formation.

Trace Elements in Apatite as Genetic Indicators of the Evate Apatite-Magnetite Deposit, NE Mozambique

The Evate deposit is a Neoproterozoic (~590 Ma) magnetite-apatite-carbonate body emplaced parallel to foliation of the Monapo granulite complex in NE Mozambique. A complicated history of the deposit is recorded in apatite textures visualized in cathodoluminescence (CL) images. In spite of different solid and fluid inclusions, mineral assemblages, and the CL textures, electron probe microanalyses indicate relatively consistent apatite compositions corresponding to fluorapatite (XF = 0.51–0.73, XOH = 0.21–0.47, XCl = 0.02–0.06) with limited belovite- and cesanite-type substitutions. Laser ablation inductively coupled plasma mass spectrometric analyses show that apatites from unaltered magnetite-forsterite-spinel ores are depleted in Y, REE, Ba, and Sr compared to apatites from carbonate-anhydrite ores. Hydrothermally overprinted apatites with complex patchy domain CL textures are enriched in Y-REE in greenish-grey zones, Fe-U-Th in blue zones, and Mn-Sr-Ba in brown domains. Observed CL-emissions in the Evate apatites result from very subtle variations in REE, Mn, and U contents controlled by the variability of redox conditions. The decreased Th:U ratio in the hydrothermally overprinted apatites reflects the oxidation and partial removal of U4+ from the apatite structure during the interaction with oxidizing aqueous fluids capable of transporting U6+. Flat, LREE (La-Sm)-enriched chondrite-normalized patterns with Eu/Eu* = 0.7–1.4 and Ce/Ce* = 0.9–1.5, together with concentrations of diagnostic trace elements (Sr, Mn, Y, REE) are consistent with apatites from magmatic carbonatites and phoscorites. This study corroborates that the Evate deposit is a post-collisional orogenic carbonatite genetically linked with mafic plutonic rocks intruding the Monapo granulite complex after granulite-facies metamorphism, and later overprinted by intensive hydrothermalism. The Evate apatite is peculiar in retaining its pristine magmatic signature despite the extensive hydrothermal-metasomatic alteration accompanied by dissolution-reprecipitation.

Identifying hydrothermal quartz vein generations in the Taiyangshan porphyry Cu-Mo deposit (West Qinling, China) using cathodoluminescence, trace element geochemistry, and fluid inclusions

Porphyry-style mineralization is characterized by superposition of multiple generations of quartz growth, punctuated by dissolution and juxtaposed within a single vein. Such superposition inevitably obscures temporal relationships between quartz formation, alteration events, and fluid inclusion assemblages (FIAs), and consequently complicates the interpretation of fluid origin and evolution. Very detailed information of these relationships recorded within hydrothermal quartz from the Taiyangshan porphyry Cu-Mo deposit (NW China) is obtained using integrated cathodoluminescence (CL) imaging, trace element analyses, and fluid inclusion petrography.The CL characteristics range from bright blue-CL quartz (Q1) associated with early high-temperature potassic alteration, to dark blue-CL quartz (Q2) broadly coinciding with metal precipitation, to post-ore dull red-CL fine-grained, anhedral, and recrystallized quartz (Q3) subgrains. Early bright blue-CL quartz (Q1) crystals, generally at the edges of stockwork veinlets close to wallrock, are characterized by oscillatory growth zoning, and exhibit alignment of primary, equant-shaped, brine-bearing FIAs along the banded growth zones. Later dark blue-CL quartz (Q2) crystals are generally euhedral in shape and grow with c-axes pointing inward to the vein center. They exhibit well-defined, but rarely preserved, growth zones truncating Q1 and crystal terminations projecting into pyrite and chalcopyrite in the vein center although they are not spatially associated with sulfides. These vein features clearly indicate that Q2 crystals grow into an open cavity or fracture during the ore precipitation. This is also evident by coexisting, secondary, irregular-shaped, liquid-rich inclusions and vapor-rich inclusions along fractures transecting Q1 oscillatory growth bands. The coexistence of hypersaline and vapor-rich inclusions moreover provides unequivocal evidence for phase separation during mineralization. Dull red-CL quartz (Q3) crystals appear to coincide with or follow sericitic alteration, and cut and encompass preexisting Q1 and Q2 crystals. They spatially associated with sulfides. The Q3 grains contain rare well-defined FIAs, but show scattered, secondary, irregular-shaped, low-salinity aqueous inclusions with small- to medium-sized vapor bubbles (10–30 vol%), as well as complex fluid inclusions that have migrated to the margins of anhedral Q3 subgrains due to quartz dissolution and recrystallization.Formation of early blue-CL Q1 and Q2 crystals at moderate temperatures are consistent with enrichment of Ti in the quartz lattice compared to neighboring younger Q3. The Q2 crystals are typified by elevated concentrations of Al and K concentrations when compared to Q1 and Q3. The substitution of Ti4+ for Si4+ in the tetrahedral sites of quartz leads to an increased CL intensity from Q1, to Q2, and then to Q3 corresponding to a decrease in quartz precipitation temperature. Ore deposition, recorded by integration of CL textures, FIAs petrography, and trace element variations in Q2, in the Taiyangshan porphyry Cu-Mo deposit must have occurred over a significant change in physicochemical conditions. This suggests that phase separation due to fluid cooling/pressure drops during the transition from lithostatic to hydrostatic regimes is critical to porphyry mineralization. We further propose a complex hydrothermal quartz vein formation history involving multiple fluid inclusions under varying pressure and temperature conditions.

Combined Zircon, Molybdenite, and Cassiterite Geochronology and Cassiterite Geochemistry of the Kuntabin Tin-Tungsten Deposit in Myanmar

AbstractThe Kuntabin Sn-W deposit, located in southern Myanmar, is characterized by abundant greisen-type and quartz vein-type cassiterite and wolframite mineralization. We have conducted multiple geochronological methods and isotope and trace element analyses to reveal the age and evolution of the Kuntabin magmatichydrothermal system.Zircon U-Pb dating of the two-mica granite yielded a weighted mean 206Pb/238U age of 90.1 ± 0.7 Ma. Cassiterite U-Pb dating provided a lower intercept age of 88.1 ± 1.9 Ma in the Tera-Wasserburg U-Pb concordia diagram. Molybdenite Re-Os dating returned a weighted mean model age of 87.7 ± 0.5 Ma and an isochron age of 88.7 ± 2.7 Ma. These ages indicate a genetic relationship between granite and Sn-W mineralization in the Kuntabin deposit and record the earliest magmatism and Sn-W mineralization in the Sibumasu and Tengchong terranes related to subduction of the Neo-Tethys oceanic slab. Three generations of cassiterite have been identified with distinctive cathodoluminescence textures and trace element patterns, indicating the episodic input of ore-forming fluids and distinctive changes in the physical-chemical conditions of the Kuntabin magmatichydrothermal system. Sudden changes of fluid pressure, temperature, pH, etc., may have facilitated the deposition of Sn and W. Rhenium contents of molybdenite from the Kuntabin deposit and many other Sn-W deposits in Myanmar are characteristically low compared to porphyry Cu-Mo-(Au) deposits worldwide. In combination with zircon Hf isotope signatures, we infer that granites associated with Sn-W deposits in Myanmar were predominantly derived by melting of ancient continental crust and contain minimal mantle contribution.Subduction of the Neo-Tethys oceanic slab from west of the West Burma terrane reached beneath the Sibumasu terrane and led to magmatism and Sn-W mineralization at ~90 Ma when the Kuntabin deposit was formed. The Paleoproterozoic Sibumasu crust was activated during the subduction-related magmatism to form predominantly crust derived melts. After a high degree of fractional crystallization and fluid exsolution, physical-chemical changes of the hydrothermal fluid resulted in Sn and W precipitation to form the Kuntabin Sn-W deposit.

Apatite trace element geochemistry and cathodoluminescent textures—A comparison between regional magmatism and the Pea Ridge IOAREE and Boss IOCG deposits, southeastern Missouri iron metallogenic province, USA

The southeast Missouri iron metallogenic province contains a remarkable wealth of historically important Fe, Cu, Au, and rare earth element (REE) deposits including the Pea Ridge iron oxide-apatite-rare earth element (IOA-REE) deposit and the Boss iron oxide-copper–gold (IOCG) deposit. These deposits are coeval with silicic and intermediate composition magmatism in the St. Francois Mountains terrane. Magmatism, iron-oxide (±Cu, Au, Co) and apatite formation, and REE mineralization overlapped in space and time, but the specific role of regional magmatism in the metallogenesis of these deposits remains unclear and basic petrogenetic models are still debated.We report results from high-spatial resolution textural and geochemical analyses of apatite from regional igneous and ore rocks to elucidate their petrogenetic histories and evaluate deposit models. Backscattered electron and spectral cathodoluminescence imaging of apatite reveal no primary igneous zoning, but show different domains with intricate rims and dissolution/reprecipitation textures, each with distinctive REE patterns in many samples. Apatite from all samples are nearly endmember fluorapatite containing up to ∼1.3 wt% Cl and F/Cl ratios span nearly three orders of magnitude. Fresh igneous fluorapatite contain low Na2O (≤0.15 wt%) while most Pea Ridge ore samples contain higher Na2O (up to ∼0.45 wt%), and concentrations of sulfur in fluorapatite of all types are generally moderate to low (≤0.3 wt% SO3). Significant amounts of Fe (≤60,000 ppm), Mg (≤30,000 ppm), Mn (≤7000 ppm), and Sr (≤12,000 ppm) are contained in fluorapatite of all sample types, and they also have moderate amounts of As (≤4000 ppm), Ba (≤2000 ppm), Th (≤400 ppm), and U (≤80 ppm). Fluorapatite show an extraordinarily large range of ΣREE (∼0.1–2.0 wt%) and Y (∼100–7000 ppm) concentrations. While fresh igneous fluorapatite share many geochemical features with metasomatized igneous fluorapatite and ore-stage fluorapatite from the Pea Ridge IOA and Boss IOCG ore zones, they also have distinct geochemical signatures that are indicative of unique trace element partitioning and substitution mechanisms. These distinguishing textural and geochemical signatures preclude ore-zone fluorapatite genesis directly from a magma (i.e., crystallization directly from a silicate melt) but are permissive of ore-zone fluorapatite formation by magmatic-hydrothermal fluids derived from the regional magmas. Basinal brines may play an important role in the formation of fluorapatite, especially from the Pea Ridge hematite and Boss magnetite-rich zones. Fluorapatite from different ore zones likely formed by crystallization during pulses of hydrothermal fluids with varying Cl-, Na-, and F-contents, which fundamentally controlled the carrying capacity and solubility of ΣREE + Y and generated geochemically distinctive generations of fluorapatite.Exploration geologists using fluorapatite trace element geochemistry to identify IOA and IOCG deposits should proceed with caution, as more high-quality data from these deposits are needed to improve multivariate discrimination analysis. Fluorapatite from IOA/IOCG deposits can be reasonably discriminated from that of other mineral deposit types (e.g., porphyry/epithermal, skarn, orogenic), but no criteria successfully discriminate yet between IOA and IOCG deposits.

Genesis of the Xiaolonghe quartz vein type Sn deposit, SW China: Insights from cathodoluminescence textures and trace elements of quartz, fluid inclusions, and oxygen isotopes

Quartz textures revealed by scanning electron microscope cathodoluminescence (SEM–CL) images suggest that quartz in the Xiaolonghe Sn deposit formed in at least three fluid episodes. Quartz (Q1) in the pre-ore silicification zone has homogeneous texture, high CL intensity and high Ti content (19–53 ppm). Fluid inclusions hosted in Q1 are vapor-rich (V1-type) and homogenized as supercritical fluid at ∼570 °C. Quartz (Q2) in the syn-ore topaz-cassiterite-quartz veins has lower CL intensity and is characterized by euhedral growth zones with lower Ti content (1.3–12 ppm). Fluid inclusions hosted in Q2, topaz and cassiterite are liquid-rich fluid inclusions of moderate salinity (∼15 wt% NaCl equiv) (L1-type) which homogenized at ∼423 °C. The post-ore quartz (Q3) closely associated with sericitization of topaz generally crosscuts Q2, and has dark CL intensity and much lower Ti concentration (<1.5 ppm). In Q3, the vapor-rich (V2-type) fluid inclusions coexist with the halite-bearing (S-type) fluid inclusions, which homogenized at ∼269 °C, 0.05 kbars.The upper limits of T–P conditions of pre-ore and syn-ore stage are constrained by the intersection of NaCl–H2O fluid inclusion isochores and Ti-in-quartz isopleths, and the lower limits are based on microthermometry results of fluid inclusions. Combined with the δ18Ofluid value (8.3‰) of Q1, it indicates that the pre-ore supercritical fluid was directly exsolved from a granitic magma at T = 570–600 °C and P = 0.70–0.77 kbars, corresponding to a maximum depth of 2.8 km under lithostatic pressure. The syn-ore subcritical fluid (8.0‰ > δ18Ofluid > 6.3‰) mixed with some meteoric water was under 423–450 °C, 0.32–0.45 kbars. The transition from the pre-ore supercritical fluid to the syn-ore subcritical fluid indicates boiling condition (probably at 512 °C, 0.62 kbars), which was likely caused by hydraulic fracturing under high pressure. Both the fluid boiling and fluid mixing contribute to the cassiterite precipitation in Xiaolonghe Sn deposit. In the post-ore stage, the coexisting S-type and V2-type fluid inclusions in Q3 indicates a second fluid boiling at 269 °C, 0.05 kbars, which was probably caused by decompression due to rapid denudation of the overlain strata. The low salinity (5.5 wt% NaCl equiv) L2-type fluid inclusions hosted in fluorite homogenized at 199 °C and <0.02 kbars, indicating that fluorite veins probably formed in open fractures. The δ18Ofluid results from sericite (5.1–5.0‰), quartz (−1.3 to −2.0‰), and chlorite (−7.9‰) suggest that increasing meteoric water was involved after second fluid boiling.

Ghosts of Apatite Past: Using Hyperspectral Cathodoluminescence and Micro-Geochemical Data To Reveal Multi-Generational Apatite in the Gifford Creek Carbonatite Complex, Australia

Apatite can host significant levels of trace elements, including REE, within its crystal lattice, making it particularly useful for deciphering geological events and processes. This study employs hyperspectral cathodoluminescence (CL) and in situ microchemical techniques to identify and characterize various generations of apatite occurring in the phoscorites, carbonatites, and fenites of the Gifford Creek Carbonatite Complex (GCCC), Western Australia. Hyperspectral CL revealed that apatite crystals in all samples have complex internal zoning, including multiple distinct generations, with zones of relatively bright CL generally having more complex spectra compared to darker CL zones. Most of the CL spectra have prominent sharp peaks at similar to 1.4 eV and similar to 2.l eV as well as a broad peak between 2.3 eV and 3.5 eV. We relate these different peaks to individual REE activators and groups of activators, in particular Nd3+, Eu3+, Sm3+, and Ce3+. Trace element analyses of apatite confirm the relative enrichment of REE in the CL brighter zones. Most apatite generations exhibit concave-down to sinusoidal REY patterns lacking Eu anomalies, but often feature distinct negative Y anomalies. The depletion in LREE is interpreted to be due to LREE sequestration into monazite, which is relatively abundant in most of the samples. Most apatite samples contain very low Si contents, but appreciable Na, so REE incorporation into apatite was primarily via a coupled substitution of REE + Na replacing 2Ca, which is consistent with the highly alkaline, low SiO(2 )environment under which the apatite formed. Based on the combined trace-element signatures and CL textures, we interpret the multiple generations of apatite to reflect magmatic growth from alkaline magmas followed by recrystallization during subsequent metamorphic/hydrothermal events. The notable exception is the apatite core domains from a fenite sample that contain relatively high Si and Mn contents, low Sr, and relatively HREE-enriched REY patterns with distinct negative Eu anomalies. This apatite is interpreted to be relict from the granitic precursor to fenitization. The apatite samples also show systematic compositional variations across the GCCC, with apatite from phoscorite samples from the southeast part of the complex containing higher Sr, lower Gd/Ce, and lower lambda(3 )values (normalized REE pattern inflections) compared to apatite from the northwest part of the complex. Recognition of these spatial variations in apatite compositions from the intra-grain micro-scale through to the district scale demonstrates the utility of combining advanced petrographic methods, such as hyperspectral CL, with micro-chemical analysis to reveal complex geological records preserved in apatite. As apatite is a common accessory mineral, these techniques may be more broadly applicable to igneous source tracing, understanding metamorphic and/or metasomatic processes, provenance studies from detrital mineral records, and studies of the evolution of ore systems.

Laurite and zircon from the Finero chromitites (Italy): New insights into evolution of the subcontinental mantle

Chromitites enclosed within metasomatised Finero phlogopite peridotite (FPP) contain accessory platinum-group minerals, base metal (BM) sulfides, baddeleyite, zircon, zirconolite, uraninite and thorianite. To provide new insights into mantle-crustal interaction in the Finero lithosphere this study evaluates (1) the mineral chemistry and Os-isotope composition of laurite, (2) the crystal morphology, internal structure, in-situ U-Pb, trace-element and Hf-isotope data of zircon from two chromitite localities at Alpe Polunia and Rio Creves. The osmium isotope results reveal a resticted range of ‘unradiogenic’ 187Os/188Os values for laurite at Alpe Polunia (0.1247–0.1251, mean 0.1249±0.0001). Re-Os model ages (TRD) of laurite reflect an Early Paleozoic partial melting event (ca 450Ma or older), presumably before the Variscan orogeny. The Os isotopic composition of laurite/chromitite probably preserves their mantle signature and was not affected by later metasomatic processes. U-Pb and Hf-isotope data show that the Finero chromitites have distinct zircon populations with peculiar morphology, internal cathodoluminescence textures, trace-element composition and an overall U-Pb age span from ∼310Ma to 190Ma. Three age peaks at Rio Creves (220±4Ma, 234.2±4.5Ma and 277.5±3.2Ma) are consistent with a prolonged formation and multistage zircon growth, in contrast to the common assumption of a single metasomatic event during chromitite formation. The trace-element signatures of zircons are comparable with those of mantle-derived zircons from alkaline ultramafic rocks, supporting the carbonatitic nature of the metasomatism. Hf-isotope compositions of the Finero zircons, with εHf values ranging mainly from −3 to +1, are consistent with crustal input during metasomatism and could indicate that the parental melts/fluids were derived from a relatively old source; the minimum estimates for Hf model ages are 0.8–1.0Ga. Our findings imply that mantle rocks and metasomatic events at Finero have a far more complex geological history than is commonly assumed.

Physical and Chemical Evolution of the Dabaoshan Porphyry Mo Deposit, South China: Insights from Fluid Inclusions, Cathodoluminescence, and Trace Elements in Quartz

The Dabaoshan polymetallic deposits in the Nanling Range, South China, consist of porphyry and skarn-type Mo mineralization genetically related to Jurassic porphyritic intrusions and adjacent strata-bound Cu-Pb-Zn mineralization hosted in mid-Devonian limestone. Porphyry Mo mineralization is characterized by the superposition of multiple generations of crosscutting quartz-bearing veins including: barren quartz veins (V1), quartz-molybdenite veins with K-feldspar alteration halos that host the bulk of the Mo mineralization (V2), quartz-pyrite veins with muscovite alteration (V3), and late base metal mineralization with argillic alteration (V4), as well as limestone-hosted strata-bound Cu-Pb-Zn mineralization (VS). Fluid inclusion petrography and microthermometry combined with cathodoluminescent textures and trace elements in quartz reveal changes in pressure and temperature of the hydrothermal system that formed the deposit. V1 and V2 veins are dominated by low-salinity (1–6 wt % NaCl equiv), CO 2 -bearing (4–10 mol %) two-phase inclusions with about 35 vol % bubble trapped in the one-phase field above the solvus of the fluid. V1 veins are dominated by CL-bright granular quartz mosaics with higher CL intensity than any other vein type. This quartz also contains more Ti than any other vein generation (24–89 ppm), while Al, Ge, and Li concentrations overlap with other vein generations. Molybdenum ore-hosting V2 veins are also dominated by CL-bright granular quartz mosaics, but V2 veins display slightly less CL intensity and correspondingly lower Ti concentrations (10–65 ppm). V3 veins have a broader spatial distribution than V1 and V2 veins, extending from inside the porphyries out into the adjacent limestone. These veins are also dominated by low-salinity (2–6 wt % NaCl equiv), CO 2 -bearing (4–7 mol %) two-phase inclusions, these containing about 45 vol % bubble trapped above their solvus. V3 veins are dominated by CL-dark quartz with euhedral growth zones of oscillating CL intensity and systematically lower Ti concentrations than previous vein generations (1.5–12 ppm). Minor V4 veins cut all the above vein generations and also occur as late infill in V3 veins. Low-salinity (4–7 wt % NaCl equiv), CO 2 -bearing (4–5 mol %) two-phase inclusions with about 20 vol % bubble prevail in V4 veins. V4 veins have the lowest CL-intensity quartz of all vein types, with euhedral growth zones of oscillating CL intensity and the lowest Ti concentration of all vein types (0.54–5.3 ppm). Intersections of fluid inclusion isochores with Ti-in-quartz isopleths indicate that the hydrothermal system evolved from near-magmatic pressures and temperatures of 2.7 ± 0.2 kbars and 650° ± 40°C for V1 veins to 1.9 ± 0.2 kbars and 530° ± 40°C for V2 veins to 0.65 ± 0.2 kbars and 400° ± 40°C for V3 veins. V4 veins, which lack rutile, formed as the system cooled to 250° to 300°C at maximum pressures of 0.40 to 0.65 kbar. Unlike nearly all other reported porphyry-type ore deposits, quartz-bearing veins from the Dabaoshan porphyry Mo deposit contain few halite-bearing or vapor-dominated fluid inclusions in any vein type. The dearth of such fluid inclusions, coupled with the abundance of two- and three-phase CO 2 -bearing low-salinity fluid inclusions in all vein types is evidence that the formation conditions of V1 to V4 veins remained above the V-L surface in the H 2 O-NaCl-CO 2 system, such that fluid unmixing rarely occurred in the Dabaoshan hydrothermal system. This is further supported by only rare evidence for quartz dissolution textures in all vein types, implying that pressures were dominantly higher than zone of retrograde quartz solubility. Taken together, the fluid inclusions, CL textures, and quartz trace element data indicate that the Dabaoshan porphyry Mo deposit is one of the deepest formed porphyry-type ore deposits, having formed at depths of 6 to 7 km below surface. The extreme depth and lack of fluid unmixing inhibited Cu precipitation in the porphyry system, and instead allowed Cu to remain in solution to precipitate with Pb and Zn upon interaction with the surrounding Devonian limestone.

On the Relationship Between Cathodoluminescence and the Chemical Composition of Scheelite From Geologically Diverse Ore-Deposit Environments

Abstract The relationship between cathodoluminescence (CL) response and chemical composition of scheelite from a variety of ore-deposit settings ( e.g ., orogenic Au, skarn, porphyry-related, greisens, VMS) was investigated using SEM-EDS, CL imaging, and LA-ICP-MS techniques. Our detailed study concentrates on five samples of scheelite from a range of ore-deposit settings, including orogenic Au, skarn, VMS, and greisen deposits, but draws on a yet unpublished data base of more than 39 deposits world-wide. Results indicate that the scheelite zonation patterns observed under CL can be useful in discriminating between scheelite arising from differing mineralized environments. Scheelite from orogenic Au deposits exhibits a homogenous CL response in contrast to that from proximal intrusion-related systems, such as porphyries, skarns, and greisens that show a strong oscillatory zonation, with individual zones ranging from 300 μm in width. Results from LA-ICP-MS analyses show significant chemical variations in scheelite with respect to Mo, Sr, As, and ΣREE + Y. Maps generated from CL imaging and LA-ICP-MS data reveal a strong negative correlation between the intensity of the CL response in scheelite and Mo content. While enrichments of Sr, As, and ΣREE + Y are noted, none exhibit a correlatable effect with CL response. Furthermore, the qualitative Mo and W X-ray maps produced via SEM-EDS correlate with the corresponding LA-ICP-MS maps of the scheelite grain, successively delineating the zonation patterns observed under CL. This work also demonstrates that the combination of CL and LA-ICP-MS mapping is a powerful tool in the discussion of observed CL textures, elemental relationships, mineral growth history, and paragenesis.