Assinatura magmática-hidrotermal com base em isótopos de enxofre, do depósito filonar do Paraíba e do Alvo disseminado X1, Província Mineral de Alta Floresta (MT)

In the eastern-southeast sector of Alta Floresta Gold Province (Amazon Craton), the 1.78 – 1.77 Ga calc-alkaline magmatism is interpreted as answerable for ore-forming processes responsible for its disseminated, vein-type, and filonar gold occurrences hosted in 2.05 – 1.77 Ga units. The Aguinaldo structurally-controlled gold occurrence exhibits ore zones hosted in 0.5 – 1.5m thick quartz + sulfide ± carbonate veins crosscutting the porphyroblastic mylonite orthogneiss, with SHRIMP U-Pb-zircon concordia crystallization age of 1,984.9 ± 5.2 Ma. Distal to ore zones are observed high temperature, intensive, and pervasive (1) albite-rich alteration, followed by (2) K-Feldspar alteration, telescoped by lower temperature pervasive alterations: (3) sericite-muscovite alteration, (4) silicification and silica infills; (5) carbonate alteration, (6) chlorite alteration, and (7) late veinlet-type quartz. The silica injection represents one of the major hydrothermal stages due to generating barren quartz veins and quartz ± carbonate vein with chalcopyrite + pyrite ± gold ± silver ± sphalerite ± galena ± bismuthinite veins. Although the veins are partially deformed, local comb-quartz texture remains preserved. Gold occurs as small inclusions or in contact with pyrite and chalcopyrite, and subordinately, in sphalerite. Electron microprobe analysis indicates chlorite of brunsvigite composition formed between 242° and 420° C, whereas white mica shows low phengite contents. The polymetallic veins signature, the high chalcopyrite contents with galena and sphalerite inclusions, the comb-texture quartz veins, together with the hydrothermal alteration sequence, suggest low to moderate temperature, neutral to slightly alkaline pH, and moderate ƒO2 and ƒS2 conditions, possibly triggered by boiling process. This scenario indicates intermediate-sulfidation epithermal ore-forming processes as the responsible for the genesis of Aguinaldo gold occurrence.

Gold distribution and source of the J4 gold-bearing breccia pipe in the Qiyugou district, North China Craton: Constraints from ore mineralogy and in situ analysis of trace elements and S-Pb isotopes

Fluid mixing across unconformities between crystalline basement and overlying sedimentary basins is commonly invoked as an efficient chemical mechanism for ore deposition, but the origin of basement brines and the process of ore formation have rarely been linked by direct evidence. Using laser ablation–inductively coupled plasma–mass spectrometry microanalysis of individual fluid inclusions with an improved detection approach for anion components, we determined simultaneously the ore metal concentrations and the Cl/Br ratio in texturally well constrained inclusion assemblages from a basement-hosted quartz-fluorite-barite-Pb-Zn vein system. An inverse correlation between the Pb + Zn concentrations and the Cl/Br mass ratios in the fluid inclusions provides clear evidence for mixing of a basement-derived metal-rich brine and a metal-poor formation water that acquired its salinity from halite dissolution in Triassic evaporites of the sedimentary cover. This mixing of two distinct brines with comparable salinity is recorded during the growth of individual quartz crystals containing small galena inclusions, demonstrating the transient and episodic nature of fluid mixing during mineral deposition.

The paper considers processes of ore formation. This concerns complex dynamic natural objects, depending on polygenic geological phenomena, mutually interacting and forming a single mineral formation environment. Development of ore-forming systems is connected not only with the natural evolution of thermodynamic parameters, but also with physical-chemical properties and composition of ore-bearing deposits, state and character of manifestation of tectonic structures, such as field strength, degree of tectonic transformation of rocks, dynamometamorphism and others. Influence of postmagmatic fluids and other factors on the process of mineral formation is also considered. Mineral formation at gold deposits is the result of the interaction of various polygenic geological processes that ultimately determine the character of mineralisation at the deposits. Experimental studies cannot fully reconstruct the conditions of ore formation. Therefore, it is necessary to apply the method of recalculation of thermodynamic constants.

In situ multiple sulfur isotope analysis by SIMS of pyrite, chalcopyrite, pyrrhotite, and pentlandite to refine magmatic ore genetic models

Yuhengtang is a representative slate-hosted Au deposit in the Jiangnan orogenic belt, South China, with a reserve of ~55 t Au and an average grade of ~3.9 g/t. Gold mineralization is characterized by veinlet and disseminated ores comprising native gold, auriferous pyrite, and arsenopyrite. Paragenesis of the Yuhengtang deposit can be divided into three stages. Pre-ore stage 1 is composed of bedding-parallel layers of pyrite in slate of the Neoproterozoic Banxi Group. Main ore stage 2 represents the Au mineralization stage, and two distinct types of mineralization can be distinguished: visible Au-arsenopyrite-pyrite in quartz veinlets and auriferous arsenopyrite-pyrite disseminated within altered slate. Post-ore stage 3 consists of quartz-pyrite-calcite-ankerite veins. In this study, we integrate electron microprobe, laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and high-resolution ion microprobe (SHRIMP) analyses to document textural, isotopic, and compositional variation among texturally complex pyrite and arsenopyrite assemblages in veinlet and disseminated ores. Additionally, LA-ICP-MS sulfur isotope mapping of pyrite highlights the covariation behavior between trace elements and sulfur isotopes at the grain scale, thus allowing the factors controlling sulfur isotope fractionation in hydrothermal Au deposits to be constrained. Pyrite, of sedimentary origin (stage 1), hosts negligible Au (<1.6 ppm) but is enriched in δ34S (15.6–25.8‰). Pyrite and arsenopyrite from stage 2 veinlet mineralization both display porous and dissolution-reprecipitation textures, have low Au concentrations (<4 and <78 ppm, respectively), and show a large variation in δ34S (–2.7 to 14.7‰ and –10.3 to 12.1‰, respectively). Pyrite and arsenopyrite from disseminated mineralization are, in contrast, characterized by oscillatory zoning textures and homogeneous appearance in backscattered electron (BSE) images, respectively, and are obvious by their relatively high contents of invisible Au (up to 90 and 263 ppm, respectively) and restricted range of δ34S values (0–5.3‰). These data suggest that magmatic-hydrothermal fluids contribute most of the Au and S budget in the Yuhengtang Au deposit. The major differences between veinlet and disseminated mineralization in terms of texture, trace element concentrations, and δ34S signatures of pyrite and arsenopyrite reflect contrasting mechanisms of Au precipitation and an evolution of physicochemical parameters of the ore-forming processes, particularly fO2 and the intensity of fluid-rock interaction. Pyrite from stage 3 appears homogeneous in BSE images yet displays a wide variation in δ34S values (1.2–31.4‰), further highlighting the controlling role played by physicochemical condition (i.e., pressure) on the δ34S signature of sulfides. Results of the coupled LA-ICP-MS sulfur and trace element mapping reveal that some zoned pyrite grains from stage 2 formed via overgrowth of Au-rich, light δ34S (2.4‰) hydrothermal rims onto Au-poor, heavy δ34S (18.1–18.5‰) sedimentary cores. All results support that multiple depositional mechanisms within a dynamic mineral system were responsible for Au concentration and define the specific textural, compositional, and sulfur isotope signatures of sulfides in coexisting vein/veinlet and disseminated mineralization. The new data highlight the ore-forming processes-based interpretation for ore genesis and underpin the importance of performing complementary in situ mineralogical analyses to elucidate the source and evolution of ore-forming fluids and enable correct interpretation of the architecture of the hydrothermal Au system.

More than half of the 25 largest known porphyry copper deposits, defined in terms of contained copper metal, formed during three time periods: the Paleocene to Eocene, Eocene to Oligocene, and middle Miocene to Pliocene. These giant deposits are clustered within three provinces, central Chile, northern Chile, and southwest Arizona-northern Mexico. Other giant deposits occur in Montana, Utah, Panama, Peru, Argentina, Irian Jaya, Mongolia, and Iran. Compressive tectonic environments, thickened continental crust, and active uplift and erosion were associated with the formation of many of these deposits. Calc-alkalic magmas are most favorable for the formation of giant porphyry copper deposits, although several of the largest systems are associated with high K calc-alkalic intrusions. The 25 largest gold-rich porphyry deposits are concentrated in the southwest Pacific and South America, with other occurrences in Eurasia, British Columbia, Alaska, and New South Wales. Many of the deposits formed in the last 13 m.y. The largest of the deposits are associated with high K calc-alkalic intrusions. Many calc-alkalic porphyritic intrusions have also produced giant gold-rich porphyries. In the last 20 m.y., the formation of giant porphyry copper-molybdenum and copper-gold deposits in the circum-Pacific region has been closely associated with subduction of aseismic ridges, seamount chains, and oceanic plateaus beneath oceanic island and continental arcs. In several examples, these tectonic perturbations have promoted flat-slab subduction, crustal thickening, uplift and erosion, and adakitic magmatism coeval with the formation of well-endowed porphyry and/or epithermal mineral provinces. Similar tectonic features are inferred to be associated with the giant porphyry copper-molybdenum provinces of northern Chile (Eocene-Oligocene) and southwest United States (Cretaceous-Paleocene). Topographic and thermal anomalies on the downgoing slab appear to act as tectonic triggers for porphyry ore formation. Other factors, such as sutures in the overriding plate, permeability architecture of the upper crust, efficient processes of ore transport and deposition, and, in some cases, formation and preservation of supergene enrichment blankets are also vital for the development of high-grade giant ore deposits. A low-grade geochemical anomaly may be the final product of mineralization, if ore-forming processes do not operate efficiently, even in the most favorable geodynamic settings.

The absence of a genetic classification of ore-forming processes is the result of a rather slow-paced accumulation of knowledge in ore-forming processes, which, in its turn, could be explained by objective conditions such as the fact that during the last few decades the genetic classification included only the description of mineral deposits. The existing genetic mineral deposit classifications has developed and embraced the genetic classification of ore-forming processes in accordance with system theory, structured taxons revealing the nature of the processes and the basis- information source of these processes. The base involved the developed model system of ore mineralization- ore formations (geological formations with syngenetic mineralization) within poly-component and mono-component subformations; for convergent mineralization- geological types of deposits. The latter, as well as non-convergent subformations has accumulated all data about initiating and conditioning ore formation within wide-scaled geological processes. The geological mineralization types within ore formations and subformations are included in the genetic classification of ore-forming processes. This, in its turn, makes it possible to forecast the functions and provide a regular transition into the geological-genetic classification of ore-forming processes in accordance to above-mentioned matrix-structure, and, simultaneously, further the development of the existing geological- genetic theory of ore formation.

A model of the evolution of a massive sulphide ore-magmatic system was constructed for the Akzharsky ore field, which is based on the analysis of two groups of elements of a typical model that characterize the magmatic and ore stages of its development. According to the proposed model, the ore deposits of the Akzharsky ore field were formed by a combined method. Copper came with deep hydrothermal solutions, separated in the process of magmatic liquation at the final (ore) stage of the development of the ore-magmatic system. Sulfur also had a juvenile source, as evidenced by the closeness of its isotopic composition in pyrites to the meteorite standard, and iron was extracted from the host rocks as a result of their hydrothermal processing. The onset of the ore process is associated with the formation of propylites and the hydrothermal-sedimentary deposition of hydroxide ferrous mineralization, subsequently transformed into magnetite ores under the influence of metamorphism. Massive sulphide mineralization completes ore formation and is a product of partial processing of early hydroxide ferruginous ores by later pyrite-bearing fluids. Ore formation was shortlived and proceeded under conditions of periodically renewed volcanic activity, which contributed to the rapid burial of ores and prevented the full development of the ore cycle from the earliest to the final mineral paragenesis, as well as the creation of large massive sulphide deposits. The process of massive sulphide ore formation was short-term and onestage, which manifested itself in the relative simplicity and uniformity of the texture and structural features of the ores, telescoping of productive mineralization in a narrow vertical interval, and the absence in some cases of distinct mineral and geochemical zoning.

Felsic granulite xenoliths entrained in Miocene (~13 Ma) isotopically evolved, mantle-derived ultrapotassic volcanic (UPV) dykes in southern Tibet are refractory meta-granitoids with garnet and rutile in a near-anhydrous quartzo-feldspathic assemblage. High F–Ti (~4 wt.% TiO2 and ~3 wt.% F) phlogopite occurs as small inclusions in garnet, except for one sample where it occurs as flakes in a quartz-plagioclase-rich rock. High Si (~3.45) phengite is found as flakes in another xenolith sample. The refractory mineralogy suggests that the xenoliths underwent high-T and high-P metamorphism (800–850 °C, >15 kbar). Zircons show four main age groupings: 1.0–0.5 Ga, 50–45, 35–20, and 16–13 Ma. The oldest group is similar to common inherited zircons in the Gangdese belt, whereas the 50–45 Ma zircons match the crystallization age and juvenile character (eHf i +0.5 to +6.5) of Eocene Gangdese arc magmas. Together these two age groups indicate that a component of the xenolith was sourced from Gangdese arc rocks. The 35–20 Ma Miocene ages are derived from zircons with similar Hf–O isotopic composition as the Eocene Gangdese magmatic zircons. They also have similar steep REE curves, suggesting they grew in the absence of garnet. These zircons mark a period of early Miocene remelting of the Eocene Gangdese arc. By contrast, the youngest zircons (13.0 ± 4.9 Ma, MSWD = 1.3) are not zoned, have much lower HREE contents than the previous group, and flat HREE patterns. They also have distinctive high Th/U ratios, high zircon δ18O (+8.73–8.97 ‰) values, and extremely low eHf i (−12.7 to −9.4) values. Such evolved Hf–O isotopic compositions are similar to values of zircons from the UPV lavas that host the xenolith, and the flat REE pattern suggests that the 13 Ma zircons formed in equilibrium with garnet. Garnets from a strongly peraluminous meta-tonalite xenolith are weakly zoned or unzoned and fall into four groups, three of which are almandine-pyrope solid solutions and have low δ18O (+6 to 7.5 ‰), intermediate (δ18O +8.5 to 9.0 ‰), and high δ18O (+11.0 to 12.0 ‰). The fourth is almost pure andradite with δ18O 10–12 ‰. Both the low and intermediate δ18O groups show significant variation in Fe content, whereas the two high δ18O groups are compositionally homogeneous. We interpret these features to indicate that the low and intermediate δ18O group garnets grew in separate fractionating magmas that were brought together through magma mixing, whereas the high δ18O groups formed under high-grade metamorphic conditions accompanied by metasomatic exchange. The garnets record complex, open-system magmatic and metamorphic processes in a single rock. Based on these features, we consider that ultrapotassic magmas interacted with juvenile 35–20 Ma crust after they intruded in the deep crust (>50 km) at ~13 Ma to form hybridized Miocene granitoid magmas, leaving a refractory residue. The ~13 Ma zircons retain the original, evolved isotopic character of the ultrapotassic magmas, and the garnets record successive stages of the melting and mixing process, along with subsequent high-grade metamorphism followed by low-temperature alteration and brecciation during entrainment and ascent in a late UPV dyke. This is an excellent example of in situ crust–mantle hybridization in the deep Tibetan crust.

This study investigates the histological development of the digestive system of the common clownfish, Amphiprion percula Lacepede 1802, as a means to predict the time when the early juveniles can begin to digest inert feeds. The incubation period is completed within 7 days. At the time of hatching the alimentary canal is advanced and larvae start exogenous feeding immediately. Three days after hatch (DAH) the yolk sac is completely absorbed and at 5 DAH small supranuclear inclusions appear in the hindgut epithelium, suggesting pinocytotic digestion. At 7 DAH gastric glands are established in the epithelium of the stomach and by 9 DAH supranuclear inclusion vacuoles have appeared in the epithelium of the midgut, indicating extracellular digestion and absorption across the lumen. It was concluded that A. percula could only effectively digest artificial feeds from 9 DAH.

From the roots to the roof: An integrated model for the Neoarchean Carajás IOCG System, Brazil

O Garimpo da Raimunda está localizado na PMAF, ao sul do Cráton Amazônico, hospedado no Granito Novo Mundo. As análises feitas evidenciaram a ocorrência de duas rochas hospedeiras principais da mineralização: (1) tonalito; e (2) granodiorito. Foram reconhecidos seis estágios hidrotermais: (1) alteração sódica; (2) alteração potássica; (3) alteração sericítica; (4) alteração propilítica; (5) injeção de sílica; (6) vênulas tardias. O minério aurífero é filonar e está associado a veios de quartzo ± carbonato do 5º estágio de alteração descrito. A paragênse do minério é pirita ± calcopirita ± pirrotita ± esfalerita ± hematita ± bismutinita ± ouro. As análises sugerem que o garimpo se insere no contexto dos sistemas auríferos disseminados e confinados a veios e stockwork de quartzo em granitos descritos na província. A hipótese adotada neste trabalho é de que o sistema hidrotermal e as zonas mineralizadas do garimpo da Raimunda se formaram a partir do desenvolvimento de um sistema epitermal intermediate sulfidation que teria telescopado um possível sistema do tipo pórfiro. Palavras-chave: Província Mineral de Alta Floresta. Ouro. Alteração hidrotermal. Garimpo da Raimunda. ABSTRACT - The Raimunda mining is located in the Alta Floresta Gold Province, south of the Amazonian Craton, hosted in Granito Novo Mundo. The analyzes carried out showed the occurrence of two main host rocks of the mineralization: (1) tonalite; and (2) granodiorite. Six hydrothermal stages were recognized: (1) sodic alteration; (2) potassic; (3) seritic; (4) propylitic; (5) silica injection; e (6) late veinlets. The gold ore is confined, temporally and spatially associated with quartz ± carbonate veins, which correspond to the 5th alteration stage described. The ore is represented by the paragenesis pyrite ± chalcopyrite ± pyrrhotite ± sphalerite ± hematite ± bismuthinite ± gold. The characteristics of the Raimunda mining are similar with the disseminated gold systems confined to veins and quartz stockwork in calc-alkaline granites described in the province. The hypothesis adopted in this work is that the hydrothermal system and the sulphide and mineralized zones of the Raimunda mine formed from the development of an epithermal intermediate sulfidation system that superimposed (telescoped) a possible porphyry-type system. Keywords: Alta Floresta Mineral Province. Gold. Hydrothermal alteration. Raimunda mining.

A comprehensive study of samples from MVT–type base-metal (Zn-Pb) deposits from across the Canadian Cordillera was done to compare and contrast features and assess their relevance in the context of sulphide mineralization. Petrography and supported CL imaging indicates early host rock dissolution to form secondary fine-grained dolostone during marine cementation is followed by multiple generations of dolomite cements (low T, fine-grained to coarser, higher T varieties) that overlaps with Zn-Pb sulphides which is succeeded by a later barren calcite stage. Ore-stage dolomite is often rich in Fe (<1.3 wt. % FeO) and hosts small sphalerite inclusions. Sphalerite-hosted fluid inclusions record Th values (77–214°C) and salinities (1–28 wt. % equiv. NaCl±CaCl2) that reflect fluid mixing with no single fluid type related to sulphide mineralization. In situ SIMS δ18OVSMOW data for dolomite and calcite (13 to 33‰) suggest involvement of several fluids (i.e., seawater, basinal, meteoric) over a large temperature range at varying fluid-rock ratios. In situ SIMS δ34SVCDT data for sphalerite and pyrite indicate a large variation (8 to 33‰), but with smaller ranges (<2 to 3‰) for the settings studied, and suggest reduced S was produced dominantly via TSR processes from homogeneous sulphur reservoirs. Together the datasets suggest involvement of several fluids in the mineralizing process with mixing of a S-poor, metal-bearing fluid with a metal-poor, S-bearing fluid.

Orogenic or mesothermal quartz lodes in lower Palaeozoic Greenland Group metasedimentary rocks of the Reefton area have produced 67 tonnes (t) of gold prior to 1951, and recent exploration has identified new gold resources in several deposits, including the largest past producers, Blackwater and Globe-Progress. The metasedimentary rocks consist of alternating sandstone and mudstone beds that were metamorphosed to lower greenschist facies prior to being hydrothermally altered adjacent to the quartz lodes. The sandstones are feldspathic litharenites averaging Q65–F10–R25, with detrital grains of quartz, rock fragments, muscovite, and plagioclase and biotite that were altered to albite and chlorite, respectively, during metamorphism. Accessory minerals are graphite, apatite, zircon, tourmaline and titanite. Hydrothermal alteration of the sandstones has developed a mineral assemblage of K-mica, carbonate (dolomite, ankerite, ferroan magnesite and magnesian siderite), chlorite, pyrite and arsenopyrite. The abundance of hydrothermal chlorite is greater at Blackwater than at the other prospects studied. Hydrothermal alteration associated with the quartz lodes is marked by bleaching, magnesian siderite spots, disseminated arsenopyrite and pyrite and thin carbonate, quartz and sulphide veins. These trends are accompanied by increasing concentrations of S, As and Sb and decreasing Na, and a decrease of Fe and Mg in K-mica. The alkali alteration indices 3K/Al (representing K-mica) and Na/Al (representing albite) generally show antipathetic trends, with 3K/Al increasing near the lodes and Na/Al decreasing. These trends reflect the replacement of albite by K-mica. Carbonate alteration indices CO2/(Ca + Mg +Fe) and CO2/[Ca + Mg + Fe –0.5(S + As)] quantify the abundance of hydrothermal carbonates, but they show variable correlation with the lodes. They increase the width of the alteration halo in the hanging wall of the lodes at the Globe-Progress and General Gordon prospects, but the peak values are as far as 150 m from the lodes. By contrast, peak values of the carbonate alteration indices are within 10 and 2 m of the lodes, respectively, at the Merrijigs and Blackwater deposits. Data show that for deposits with wide hydrothermal alteration halos, such as at the Globe-Progress and General Gordon prospects, the use of a suite of geochemical indicators can assist exploration by indicating trends in hydrothermal alteration that provide vectors to mineralisation. They also increase the size of the exploration target. By contrast, the alteration halo of the Blackwater deposit is restricted to within less than 5 m of the quartz lode and, therefore, the geochemical indicators are of more limited assistance to exploration.