Tracing fluid saturation during pegmatite differentiation by studying the fluid inclusion evolution and multiphase cassiterite mineralisation of the Gatumba pegmatite dyke system (NW Rwanda)

Hulsbosch, Niels; Muchez, Philippe

doi:10.1016/j.lithos.2019.105285

Cited by 24 publications

(21 citation statements)

References 62 publications

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“…Fluorine content estimation is based on the equation F[mass%] = 0.0847 * FWHM[cm −1 ] − 0.4053 of Hulsbosch and Muchez. [ 49 ] White pixels represent spectra that were removed from the dataset because their signal reached the detector saturation. (d) CLS algorithm output map from the mapping dataset of the amblygonite–montebrasite sample from the Buranga pegmatite [Colour figure can be viewed at wileyonlinelibrary.com]…”

Section: Resultsmentioning

confidence: 99%

“…These spectral properties, especially the FWHM, are sensitive to the amount of fluorine and thus can be used to estimate the fluorine content of the mineral phase. [ 32,49 ] Figure 3c shows the estimated fluorine distribution in the sample after applying the formula F[mass%] = 0.0847 * FWHM[cm −1 ] − 0.4053 of Hulsbosch and Muchez [ 49 ] to the mapping dataset. The Buranga sample has fluorine contents ranging from 1.7 to 6.6 mol%.…”

Section: Resultsmentioning

confidence: 99%

“…[ 45–47 ] Phosphate minerals occur as polymineralic nodules at the most internal zone, or so‐called core zone, and its transition zones within the Buranga dike, which represents the last stages of magma solidification within a pegmatite dike. [ 48,49 ] Samples BU18FA09 and BU18FA19 (sample RG 9705 from the Royal Museum for Central Africa rock and mineral collection) were prepared into rectangular standard‐size 27 × 46‐mm doubly polished thick wafers and polished thin sections. To ensure sample transparency for transmitted light microscopy, the final thicknesses are adapted and vary between 30 and 50 μm for thin sections and 150–200 μm for thick wafers.…”

Section: Methodsmentioning

confidence: 99%

“…Calculation of the F content in the amblygonite–montebrasite sample of Case Study 1 used the formula F[mass%] = 0.0847 * FWHM[cm −1 ] − 0.4053 of Hulsbosch and Muchez, [ 49 ] which is an improved form of the calculations from Rondeau et al [ 32 ] The conversion from mass% to mol% considered the molar proportions of the ideal formulas of both end‐members (LiAlPO 4 F and LiAlPO 4 OH) and that the only chemical substitution in the system is the exchange of F and OH.…”

Section: Methodsmentioning

confidence: 99%

“…[ 32 ] The OH‐stretching band can thus be used to easily distinguish between the two end‐members of the series and is the most accurate way to quantify the F/OH ratio of the sample. [ 32,49 ]…”

Section: Background Informationmentioning

confidence: 99%

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High spatial resolution Raman mapping of complex mineral assemblages: Application on phosphate mineral sequences in pegmatites

Araujo

Hulsbosch

Muchez

2020

J Raman Spectroscopy

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Phosphates are a group of complex minerals widespread on Earth that can crystallize in several environments. Changes in environmental conditions during crystallization are reflected in the formation of a sequence of phosphate minerals, termed paragenesis. Accordingly, analyses of textural and chemical properties of complex mineral assemblages are essential to reconstruct the history of rocks and solid materials. Raman mapping can detect those mineralogical changes in complex assemblages with high spatial resolution, successfully determining the paragenetic sequence. Specifically, Raman spectroscopy is more advantageous than conventional methods because it requires little sample preparation, it is nondestructive, and it is capable of identifying hydrated minerals and phases composed of light elements (e.g., H and Li). In this study, the parageneses of two phosphatic assemblages from the Buranga pegmatite, a P–Li–Nb–Ta‐rich magmatic rock, are reported in detail. The first case shows the replacement of primary F‐rich montebrasite [LiAl(PO4)(OH,F)] by secondary F‐poor montebrasite [LiAl(PO4)OH]. Mapping of the OH‐stretching peak position and width identifies the mineral phases, illustrates their spatial relations, and allows to estimate the F content distribution. The second case investigates a sequence of phosphate minerals in a complex assemblage (trolleite + rosemaryite ➔ lazulite–scorzalite ➔ samuelsonite ➔ wardite). The application of multivariate analysis methods to characterize complex assemblages is assessed, and the classical least squares method is identified as the best suited for this setting. An analysis of Raman images shows that Buranga samples experienced a progressive hydration process during cooling, followed by fluid‐assisted mineral reactions with remobilization of elements, such as Ca and Na.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Background Informationmentioning

confidence: 99%

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High spatial resolution Raman mapping of complex mineral assemblages: Application on phosphate mineral sequences in pegmatites

Araujo

Hulsbosch

Muchez

2020

J Raman Spectroscopy

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Trace element composition and U-Pb ages of cassiterite from the Bolivian tin belt

et al. 2021

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The Bolivian tin belt is a metallogenic province in the Eastern Cordillera of the Andes known for its Sn, W, Ag and base metal deposits. Cassiterite, which is a major constituent in many magmatic-hydrothermal ore deposits from the Bolivian tin belt, can incorporate dozens of elements within its crystal lattice, making it a useful geological tracer mineral, and also a potential host of critical elements. New U-Pb dating of cassiterite yields Late Triassic (Kellhuani deposit) and Late Oligocene to earliest Miocene (Viloco, Huanuni and Llallagua deposits) ages. These ages confirm that Sn mineralization in the Bolivian tin belt occurred at least in two separate events during two major magmatic episodes apparently triggered by mantle upwelling, decompression melting and basalt Man crip Wi ho Track ChangeClick here to access/download;Manuscript Without Track Changes;0_Gemmrrich et al_BTB_V3.doc 2 production promoting high heat flow into the overlying crust. The composition of studied hydrothermal cassiterite yields some geochemical trends that are attributed to its distance to the causative intrusion and/or level of emplacement. For example, cassiterite is generally enriched in Nb and Ta and yields higher Ti/Zr and Ti/Sc ratios in samples from xenothermal ore deposits located adjacent to intrusive complexes relative to shallow xenothermal and epithermal ore deposits. Therefore, these geochemical trends in cassiterite are useful tracers pointing to magmatic-hydrothermal centers. REE distribution in cassiterite was likely influenced by boiling processes, which resulted in tetrad-type irregularities. Cassiterite from the Bolivian tin belt is unattractive as a source for Nb (interquartile range [IQR] 4.84-0.037 ppm), Ta (IQR 0.0924-0.0126 ppm) and Ge (IQR 3.92-0.776 ppm). Some deposits, however, contain cassiterite relatively enriched in In (IQR 96.9-9.78 ppm, up to 1414 ppm) and Ga (IQR 92.1-3.03, up to 7437 ppm), that could constitute an attractive supplementary source for these elements in addition to sulfide minerals in the same deposits.

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Geology, mineralogy, and cassiterite geochronology of the Ayawilca Zn-Pb-Ag-In-Sn-Cu deposit, Pasco, Peru

et al. 2021

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The Ayawilca deposit in Pasco, Peru, represents the most significant recent base-metal discovery in the central Andes and one of the largest undeveloped In resources globally. As of 2018, it hosts an 11.7 Mt indicated resource grading 6.9% Zn, 0.16% Pb, 15 g/t Ag, and 84 g/t In, an additional 45.0 Mt inferred resource grading 5.6% Zn, 0.23% Pb, 17 g/t Ag, and 67 g/t In, and a separate Sn-Cu-Ag inferred resource of 14.5 Mt grading 0.63% Sn, 0.21% Cu, and 18 g/t Ag. Newly obtained U-Pb dates for cassiterite by LA-ICP-MS (22.77 ± 0.41 and 23.05 ± 2.06 Ma) assign the Ayawilca deposit to the Miocene polymetallic belt of central Peru. The polymetallic mineralization occurs as up to 70-m-thick mantos hosted by carbonate rocks of the Late Triassic to Early Jurassic Pucará Group, and subordinately, as steeply dipping veins hosted by rocks of the Pucará Group and overlying Cretaceous sandstones-siltstones of the Goyllarisquizga Group. Relicts of a distal retrograde magnesian skarn and cassiterite (stage pre-A) were identified in the deepest mantos. The volumetrically most important mineralization at Ayawilca comprises a low-sulfidation assemblage (stage A) with quartz, pyrrhotite, arsenopyrite, chalcopyrite, Fe-rich sphalerite, and traces of stannite and herzenbergite. Stage A sphalerite records progressive Fe depletion, from 33 to 10 mol% FeS, which is compatible with the observed transition from low-to a subsequent intermediate-sulfidation stage (B) marked by the crystallization of abundant pyrite and marcasite. Finally, during a later intermediate-sulfidation stage (C) sphalerite (up to 11 mol% FeS), galena, native bismuth, Cu-Pb-Ag sulfosalts, siderite, Mn-Fe carbonates, kaolinite, dickite, and sericite were deposited. This paragenetic evolution shows striking similarities with that at the Cerro de Pasco Cordilleran-type polymetallic deposit, even if at Ayawilca stage C did not reach high-sulfidation conditions. The occurrence of an early retrograde skarn assemblage suggests that the manto bodies at Ayawilca formed at the transition between distal skarn and skarn-free (Cordilleran-type) carbonate-replacement mineralization. Mineral assemblages define a T-fS2 evolutionary path close to the pyrrhotite-pyrite boundary. Buffering of hydrothermal fluids by underlying Devonian carbonaceous phyllites of the Excelsior Group imposed highly reduced conditions during stage A mineralization (logfO2 < − 30 atm). The low fO2 favored efficient Sn mobility during stages pre-A and A, in contrast to other known ore deposits in the polymetallic belt of central Peru, in which the occurrence of Sn minerals is minor. Subsequent cooling, progressive sealing of vein walls, and decreasing buffering potential of the host rocks promoted the shift from low-(stage A) to intermediate-sulfidation (stages B and C) states. LA-ICP-MS analyses reveal significant In contents in Fe-rich sphalerite (up to 1.7 wt%), stannite (up to 1908 ppm), and chalcopyrite (up to 1185 ppm). The highest In content was found in stage A sphalerite that precipitated along wi...

show abstract

Tracing fluid saturation during pegmatite differentiation by studying the fluid inclusion evolution and multiphase cassiterite mineralisation of the Gatumba pegmatite dyke system (NW Rwanda)

Cited by 24 publications

References 62 publications

High spatial resolution Raman mapping of complex mineral assemblages: Application on phosphate mineral sequences in pegmatites

High spatial resolution Raman mapping of complex mineral assemblages: Application on phosphate mineral sequences in pegmatites

Trace element composition and U-Pb ages of cassiterite from the Bolivian tin belt

Geology, mineralogy, and cassiterite geochronology of the Ayawilca Zn-Pb-Ag-In-Sn-Cu deposit, Pasco, Peru

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