Muscovite Research Articles

Point and imaging spectroscopy investigations on the Pedra Branca orogenic gold deposit, Troia Massif, Northeast Brazil: Implications for mineral exploration in amphibolite metamorphic-grade terrains

The Pedra Branca gold deposit is a recent discovery conducted by private exploration companies in the Troia Massif of the northern Borborema Province, Northeast Brazil. It comprises an orogenic gold deposit hosted by the amphibolite-facies Serra das Pipocas greenstone belt. Airborne hyperspectral images (ProSpecTIR-VNIR-SWIR system) covering the Pedra Branca deposit as well as spectroscopic data (ASD-Fieldspec and SisuCHEMA instruments) from representative rock samples in the area were used in this study to investigate the spectro-mineralogical patterns of alteration minerals at both district and deposit scales, respectively. The spectroscopic data were integrated with geological information from the deposit, and also with X-ray powder diffraction and petrographic analyses, in order to reveal alteration footprints that could guide gold exploration targeting in the region. The results indicate the occurrence of a main hydrothermal calc-silicate alteration in ferromagnesian host rocks, consistent with proximal alteration assemblages found in amphibolite-facies gold deposits. White mica compositional trends suggest a later hydrothermal alteration that overprinted the pre-existing mineral assemblages and crystallized Al-rich white mica in distal zones and Al-poor white mica in the ore zone. Reflectance spectroscopy analyses of outcrop samples indicate that well-ordered kaolinite occurs as a weathering product of Al-poor white mica-bearing samples, and therefore could be used as a proxy to mineralization at the deposit scale. Mineral maps produced by processing airborne hyperspectral images, combined with soil geochemical anomalies, further support the notion that well-ordered kaolinite can be used as a proxy to mineralization in weathered ferromagnesian host rocks. Target areas for gold exploration can be defined by airborne hyperspectral data based on the identification of spectral mixtures of nontronite and well-ordered kaolinite. The mineral and physicochemical trends identified in this study set an important baseline for mineral exploration of amphibolite-facies orogenic gold deposits in greenstone belt terranes. The mineral guides defined here can be sensed by VNIR-SWIR hyperspectral sensors at multiple scales using portable, core scanning, wall-imaging, airborne or satellite-borne instruments, respectively.

Epitaxial Crystallization of Insulin on an Ordered 2D Polymer Template.

Two-dimensional polymers (2DP) are a new class of materials that consist of a monolayer of ordered molecular building blocks, which have been covalently linked. One of these monomers was self-assembled on a flat muscovite mica scaffold and subsequently the organic layer was polymerized. The resulting flat and stable 2DP layer was used as a template for protein crystallization. Crystals of insulin were epitaxially grown on the template, whereas insulin crystals grown on clean muscovite mica had a random orientation. The template was selective, considering that no epitaxially ordered crystals formed of hen egg white lysozyme, bovine serum albumin, or talin.

Direct Observation of the Orientational Anisotropy of Buried Hydroxyl Groups inside Muscovite Mica.

Muscovite mica (001) is a widely used model surface for controlling molecular assembly and a common substrate for environmental adsorption processes. The mica (001) surface displays near-trigonal symmetry, but many molecular adsorbates-including water-exhibit unequal probabilities of alignment along its three nominally equivalent lattice directions. Buried hydroxyl groups within the muscovite structure are speculated to be responsible, but direct evidence is lacking. Here, we utilize vibrational sum frequency generation spectroscopy (vSFG) to characterize the orientation and hydrogen-bonding environment of near-surface hydroxyls inside mica. Multiple distinct peaks are detected in the O-H stretch region, which we attribute to Si/Al substitution in the SiO4 tetrahedron and K+ ion adsorption above the hydroxyls based on density functional theory simulations. Our findings demonstrate that vSFG can identify the absolute orientation of -OH groups and, hence, the surface termination at a mica surface, providing a means to investigate how -OH groups influence molecular adsorption and better understand mica stacking-sequences and physical behavior.

Experimental study on the oxygenation efficiency of nano-bubble modified mineral particles at the sediment-water interface in lakes

季节性缺氧导致夏季沉积物内源磷强烈释放，加剧水体富营养化，是我国西南地区深水湖泊（水库）面临的重要挑战.有效增加夏季缺氧期深水沉积物-水界面的含氧量，是减少内源磷释放的关键.现有的深水增氧技术由于缺乏对沉积物-水界面增氧的针对性，因此治理效果有限.近年来，纳米气泡已被证实具有的稳定性好、氧传质速率高和环境风险低等优点，为新型深水增氧技术研发提供了巨大潜力.本文以天然矿物材料白云母、绢云母、硅藻土和沸石为基底，负载纳米气泡，研发纳米气泡改性矿物颗粒技术，开展湖泊沉积物-水界面增氧模拟实验研究，运用平面光电极技术评估其界面增氧效果.结果表明，纳米气泡改性矿物颗粒对沉积物-水界面具有比较明显的增氧效果.其中，改性白云母、绢云母和沸石的界面持续增氧时间可达7天以上，增氧后的界面最大溶解氧（DO）浓度达4.40 mg/L，而改性硅藻土不具有增氧能力.其次，矿物粒度对改性颗粒的增氧效果有一定影响：粒度越细，界面的最大增氧浓度越高，且持续增氧时间越长.纳米气泡改性矿物颗粒技术有望成为夏季缺氧期深水沉积物-水界面精准增氧和内源污染控制的有效技术手段.;Seasonal hypoxia that enhancing the release of phosphorus from sediment in summer and exacerbating the water eutrophication is a big challenge for deep-water lakes (reservoirs) in southwest China. Increasing the oxygen level of the sediment-water interface (SWI) during summer anoxic periods is the key to reduce the internal phosphorus release. The existing deep water oxygenation technology has limited efficiency due to lacking pertinence to the SWI. In recent years, the nano-bubbles provide great potential for the development of a new oxygenation technology, which have advantages of good stability, high oxygen mass transfer rate and low environmental risk. In this study, the natural minerals, i.e., white mica, sericite, diatomite and zeolite, were modified by nano-bubbles to develop a new oxygenation technology. Simulation experiments were conducted to assess the efficiency of the newly established oxygenation technology by using planar luminescent optode technology. Our results showed that the nano-bubbles modified mineral particles obviously increased the oxygen concentrations of the SWI. The duration of continuous oxygenation for white mica, sericite and zeolite can be over 7 days, while maximum dissolved oxygen concentration at the SWI was more than 4.40 mg/L. The modified diatomite had no ability to increase oxygen level of the SWI. Minerals with fine grain size have the stronger oxygenation efficiency and the longer oxygenation duration. The nano-bubbles modified mineral technology provides new technical support for the precise oxygenation of SWI and effective control of sediment pollution in lakes.

Geochemical Characterization of Exposed Black Shale Sediments of Matamuhari Anticline, Bangladesh

Matamuhari anticline is one of the largest anticline situated at Bandarban district of Bangladesh which is 60 km long and 20 km wide in the part of Bangladesh. Like other part of Bangladesh the whole sequence of exposed rocks of Matamuhari anticline is composed with Neogene sedimentary rocks of shale, sandstone, siltstone, silty shale, tabular and spheroidal calcareous concretions. Seven outcrop black shale samples were collected during February 2013 from the different parts of the anticline namely Boro Bari Jhiri, Ochir Jhiri and Tak Chara area were mineralogically and geochemically examined in order to better understand the depositional environment in the studied area. The major and trace elements were analyzed using XRF spectrometry. Two distinct lithofacies assemblages, mud and silty-clay are found in the collected sediments. The shales are predominated by quartz, kaolinite, chlorite, mica (muscovite and biotite), feldspar (both K-feldspar and plagioclase), and in addition to a variable ratio of vermiculite. Lithologial characteristics and geochemical data demonstrated that sediments are enriched with TOC contents ranging from 0.39 to 0.67 wt.% and shows distinctive correlation to concentration of TOC and particle size distribution. These shales are characterized by a low Mg and K as well as high Al and Fe contents. Studies also show that the values of MgO/Al2O3 and K2O/Al2O3 ratio ranges from 0.15 to 0.17 and 0.18 to 0.20 respectively. The relationship of log MgO/Al2O3 and log K2O/Al2O3 values reveals that all of the studied samples fell within the marine environment. Ni/Co ratio of the studied shale samples ranges from 2.84 to 3.88 (average 3.36). These low values of Ni/Co ratio suggest that the sediments were deposited under oxic conditions. However, the above observations suggest that the sediments of Matamuhari anticline area were deposited in a shallow marine environment under oxic conditions.

Understanding segregation processes in SAMs formed by mixtures of hydroxylated and non-hydroxylated fatty acids.

In this paper, we focus on the segregation processes emerging when preparing mixtures with different compositions of aleuritic (9,10,16 trihydroxyhexadecanoic) (ALE) and palmitic (hexadecanoic) (PAL) acids. The combination of atomic force microscopy (AFM) and molecular dynamics (MD) simulations enabled us to prove the role of the functional groups in the formation of self-assembled monolayers (SAMs) on muscovite mica surfaces. MD simulations indicate that segregation processes are favored in high ALE composition mixtures in agreement with the experimental evidence, whereas low ALE compositions promote the co-existence between segregated and dispersed systems. The secondary hydroxyl groups play a central role in the self-assembling mechanism because they control the formation of hydrogen bonding networks guarantying system stability.

A Sb ± Au mineralizing peak at 360 Ma in the Variscan belt

40Ar/39Ar absolute dating on tobelite (an ammonium-rich white mica) has been performed in order to provide geochronological constraints on the Sb ± Au mineralization and hydrothermalism at the Saint-Aubin-des-Châteaux base metal-Sb ± Au occurrence (Variscan Central Armorican Domain, France). The results show that the Sb ± Au deposition occurred atca.360 Ma. Coupled with recent results obtained in neighboring areas, this occurrence seems to belong to a large-scale Early Carboniferous economic Sb ± Au mineralizing peak in the southeastern part of the Central Armorican Domain. The emplacement of a coeval widespread mafic magmatism in the region appears to represent a major trigger for this mineralizing system at shallow depths (less than 3 km). In the light of these new data, this Early Carboniferous mafic magmatic event must be considered for the overall understanding of the genesis of mineralizing systems at the scale of the whole Variscan belt. Finally, at Saint-Aubin-des-Châteaux, evidence of an Early Permian hydrothermal event is also reported through LA-ICP-MS U-Pb dating of fluorapatite, arguing for the re-use and re-opening of Early Carboniferous mineralizing plumbing system by late (i.e.Permian) fluid flow pulses although no metal mobilization was associated with this event.

Mantle exhumation at magma-poor passive continental margins. Part I. 3D architecture and metasomatic evolution of a fossil exhumed mantle domain (Urdach lherzolite, north-western Pyrenees, France)

In two companion papers, we report the detailed geological and mineralogical study of two emblematic serpentinized ultramafic bodies of the western North Pyrenean Zone (NPZ), the Urdach massif (this paper) and the Saraillé massif (paper 2). The peridotites have been exhumed to lower crustal levels during the Cretaceous rifting period in the future NPZ. They are associated with Mesozoic pre-rift metamorphic sediments and small units of thinned Paleozoic basement that were deformed during the mantle exhumation event. Based on detailed geological cross-sections and microprobe mineralogical analyses, we describe the lithology of the two major extensional fault zones that accommodated: (i) the progressive exhumation of the lherzolites along the Cretaceous basin axis; (ii) the lateral extraction of the continental crust beneath the rift shoulders and; (iii) the decoupling of the pre-rift cover along the Upper Triassic (Keuper) evaporites and clays, allowing its gliding and conservation in the basin center. These two fault zones are the (lower) crust-mantle detachment and the (upper) cover décollement located respectively at the crust-mantle boundary and at the base of the detached pre-rift cover. The Urdach peridotites were exposed to the seafloor during the Late Albian and underwent local pervasive carbonation and crystallization of calcite in a network of orthogonal veins (ophicalcites). The carbonated serpentinized peridotites were partly covered by debris-flows carrying fragments of both the ultramafics and Paleozoic crustal rocks now forming the polymictic Urdach breccia. The mantle rocks are involved in a Pyrenean overturned fold together with thin units of crustal mylonites. Continent-derived and mantle-derived fluids that circulated along the Urdach crust-mantle detachment led to the crystallization of abundant metasomatic rocks containing quartz, calcite, Cr-rich chlorites, Cr-rich white micas and pyrite. Two samples of metasomatized material from the crust-mantle detachment yielded in situ zircon U/Pb ages of 112.9 ± 1.6 Ma and 109.4 ± 1.2 Ma, thus confirming the Late Albian age of the metasomatic event. The cover décollement is a 30-m thick fault zone which also includes metasomatic rocks of greenschist facies, such as serpentine-calcite association and listvenites, indicating large-scale fluid-rock interactions implying both ultramafic and continental material. The lowermost pre-rift cover is generally missing along the cover décollement due to tectonic disruption during mantle exhumation and continental crust elision. Locally, metasomatized and strongly tectonized Triassic remnants are found as witnesses of the sole at the base of the detached pre-rift cover. We also report the discovery of a spherulitic alkaline lava flow emplaced over the exhumed mantle. These data collectively allow to propose a reconstruction of the architecture and fluid-rock interaction history of the distal domain of the upper Cretaceous northern Iberia margin now inverted in the NPZ.

Petrology, geochemistry and P–T–t path of lawsonite‐bearing retrograded eclogites in the Changning–Menglian orogenic belt, southeast Tibetan Plateau

AbstractThe Changning–Menglian orogenic belt (CMOB) in the southeastern Tibetan Plateau, is considered as the main suture zone marking the closure of the Palaeo‐Tethys Ocean between the Indochina and Sibumasu blocks. Here, we investigate the recently discovered retrograded eclogites from this suture zone in terms of their petrological, geochemical and geochronological features, with the aim of constraining the metamorphic evolution and protolith signature. Two types of metabasites are identified: retrograded eclogites and mafic schists. The igneous precursors of the retrograded eclogites exhibit rare earth element distribution patterns and trace element abundance similar to those of ocean island basalts, and are inferred to have been derived from a basaltic seamount in an intra‐oceanic tectonic setting. In contrast, the mafic schists show geochemical affinity to arc‐related volcanics with the enrichment of Rb, Th and U, and depletion of Nb, Ta, Zr, Hf and Ti, and their protoliths possibly formed at an active continental margin tectonic setting. Retrograded eclogites are characterized by peak metamorphic mineral assemblages of garnet, omphacite, white mica, lawsonite and rutile, and underwent five‐stage metamorphic evolution, including pre‐peak prograde stage (M1) at 18–19 kbar and 400–420°C, peak lawsonite‐eclogite facies (M2) at 24–26 kbar and 520–530°C, post‐peak epidote–eclogite facies decompression stage (M3) at 13–18 kbar and 530–560°C, subsequent amphibolite facies retrogressive stage (M4) at 8–10 kbar and 530–600°C, and late greenschist facies cooling stage (M5) at 5–8 kbar and 480–490°C. Laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) U–Pb spot analyses of zircon show two distinct age groups. The magmatic zircon from both the retrograded eclogite and mafic schist yielded protolith ages of 451 ± 3 Ma, which is consistent with the ages of Early Palaeozoic ophiolitic complexes and ocean island sequences in the CMOB reported in previous studies. In contrast, metamorphic zircon from the retrograded eclogite samples yielded consistent Triassic metamorphic ages of 246 ± 2 and 245 ± 2 Ma, which can be interpreted as the timing of closure of the Palaeo‐Tethys Ocean. The compatible peak metamorphic mineral assemblages, P–T–t paths and metamorphic ages, as well as the similar protolith signatures for the eclogites in the CMOB and Longmu Co–Shuanghu suture (LCSS) suggest that the two belts formed part of a cold oceanic subduction system in the Triassic. The main suture zone of the Palaeo‐Tethyan domain extends at least 1,500 km in length from the CMOB to the LCSS in the Tibetan Plateau. The identification of lawsonite‐bearing retrograded eclogites in the CMOB provides important insights into the tectonic framework and complex geological evolution of the Palaeo‐Tethys.

Measurement of Forces between Supported Cationic Bilayers by Colloid Probe Atomic Force Microscopy: Electrolyte Concentration and Composition.

The interactions between supported cationic surfactant bilayers were measured by colloidal probe atomic force spectroscopy, and the effect of different halide salts was investigated. Di(alkylisopropylester)dimethylammonium methylsulfate (DIPEDMAMS) bilayers were fabricated by the vesicle fusion technique on muscovite mica. The interactions between the bilayers were measured in increasing concentrations of NaCl, NaBr, NaI, and CaCl2. In NaCl, the bilayer interactions were repulsive at all concentrations investigated, and the Debye length and surface potential were observed to decrease with increasing concentration. The interactions were found to follow the electrical double layer (EDL) component of DLVO theory well. However, van der Waals forces were not detected; instead, a strong hydration repulsion was observed at short separations. CaCl2 had a similar effect on the interactions as NaCl. NaBr and NaI were observed to be more efficient at decreasing surface potential than the chloride salts, with the efficacy increasing with the ionic radius.

Pietro I di Russia e la tentazione del Protestantesimo

SOMMARIO: 1. L’infanzia di Pietro - 2. Il rione degli stranieri - 3. La Grande Ambasciata - 4. L’inizio delle riforme - 5. Pietro e il monachesimo - 6. Il manifesto sulla tolleranza religiosa - 7. Pietro e la religione - 8. La subordinazione della Chiesa - 9. Feofan Prokopovyc e il suo ruolo determinante - 10. L’abolizione del Patriarcato - 11. Il Santo Sinodo governante e la paralisi della Chiesa. The Protestant Influence on the Church Reform of Peter the Great ABSTRACT: Peter the Great first comes into contact with the outside world through long familiarity with the German Quarter, a fluctuating Muscovite community of foreigners with its Lutheran and Calvinist churches, and with subsequent and extensive travel in the Protestant Lands (1697-1698), where he has ample time to appraise the role of sovereign as head of the church. The relationship of the tsar to his church is paradoxical; on the one hand, it emanates laws contrary to the principles sanctioned by the Church's Councils and organizes blasphemous parodies with The All-Joking, All-Drunken Synod of Fools and Jesters; conversely, he imposes rigidly traditional religious behaviors on the military. Rejecting his role and duty as Servant of the Salvation of Souls, he assumes a secular stance: Protector of the wellbeing of the community, ( Vsenarodnaja pol’za ). This swerve subordinating Church to sovereign undergoes elaborate scrutiny by Feofan Prokopovyc, apologist and theologian with Protestant leanings, who, in light of the abolition of the Patriarchate and the institution of the Holy Synod, affirms the principle of cuius regio eius et religio, openly challenging the position of the locum tenens Stefan Javors’kyj.

Recognition and Mapping of Structural Guides for Barytes Mineral Exploration in Parts of Kadapa District using Remote Sensing and GIS

Identification and mapping of structural criteria of a region reveals information about the occurrence of ore deposits of igneous and metamorphic origin. Remote Sensing and GIS data helps in detection of such structural features, like faults, lineament, folds, etc. These are important guides for exploration of ore mineral and groundwater. Kadapa district hosts important ore minerals of igneous and metamorphic origin like Barytes, asbestos, gold, galena, steatite etc. Barytes is exploited in the district since a long past. Present study is taken up to prepare structural map along the existing Barytes mines in the district using geospatial techniques like Remote Sensing and GIS, with an intension to identify new Barytes mineralized locations through these structural guides. The structural data of any region provides a quick payback with faster, more accurate mineral identification for gold, silver, diamonds, iron, nickel, copper, uranium, aluminum, Barytes, and also provide rock and mineral relationship in search for ore deposits during exploration. Structural criteria, is an important measure in mineral exploration of certain mineral deposits that are confined by geographic, geological and tectonic features. Mainly the occurrence of ore deposits is dependent on neighboring lithology and structural deformation of the location area. Endogenous mineral deposits like tin, muscovite, lithium, tungsten, gold, beryl, gemstones etc. are associated with intermediate and acid rocks like syenite; granite, granodiorite. etc., and deposits of copper, nickel, cobalt, silver, arsenic and apatite are formed in basic rocks like gabbro, norite, diorite, etc. Due to false nature of ore bodies and their varied controls of mineralization the techniques used for mineral exploration such as remote sensing followed by ground and airborne geophysical surveys, stream sediment, litho-geochemical surveys and core drilling have been used for regional and detailed surveys. The aspect that indicate the mineralisation are known as localizers. If these indicators can be identified on satellite data/imagery then the mineral explorations can be much faster with increased efficiency. Keywords: Multispectral, LISS-III Satellite Imagery, SOI Toposheet remote sensing, GIS Cite this Article Ramachandra M., Raghu Babu K., Pradeep Kumar B. et al. Recognition and Mapping of Structural Guides for Barytes Mineral Exploration in Parts of Kadapa District using Remote Sensing and GIS. Journal of Remote Sensing & GIS . 2018; 9(3): 30–36p.

Pathfinder Exploration Techniques Targeting Porphyry and Epithermal Alteration SystemsiIn the Temora Copper-Gold Belt

The Temora project is a key exploration target for Sandfire to discover an economic copper-gold deposit in the Lachlan Fold Belt, NSW. The district contains an Ordovician Volcanic centre that has been explored over many years and hosts a number of defined porphyry and epithermal deposits. The availability of historical drill holes meant pulps could be re-analysed for multi element geochemical data and Short Wave Infrared analysis (SWIR) data to be collected across the district. Spectral data from the white micas defined the areas of higher temperature alteration associated with mineralisation across the district. Analysis, logging and re-interpretation of the data led to the definition of a number of new targets where the systems were poorly or untested. A high priority target was defined at the Donnington prospect to the north of a small known porphyry resource on the margins of the Rain Hill intrusive complex. The target showed a potential porphyry zonation systems in the interpreted geology, alteration, SWIR analysis, geochemistry and geophysics. Drilling in the first field season intersected 120m @ 0.3 % Cu and 0.5 g/t Au from 250m with follow up drilling intersecting 77m @ 0.3 % Cu and 0.5 g/t Au from 250m around a small porphyry intrusive. Mineralisation is hosted in quartz-magnetite-feldspar-pyrite-chalcopyrite veins associated with a chlorite-magnetite-carbonate alteration. A later quartz-sericite-pyrite alteration postdates the mineralisation causing a demagnetised zone surrounding a weak magnetic high that has been used in defining the mineralisation. The mineralisation is still open and further drilling is required.

Tectonometamorphic evolution of the tip of the Himalayan metamorphic core in the Jajarkot klippe, west Nepal

AbstractNew phase equilibrium modelling, combined with U–Th/Pb petrochronology on monazite and xenotime, and 40Ar/39Ar geochronology on white mica, reveal the style of deformation and metamorphism near the southern tip of the extruded Himalayan metamorphic core (HMC). In the Jajarkot klippe, west Nepal foreland, greenschist to lower amphibolite facies metamorphism is entirely constrained to the Cenozoic Himalayan orogeny, in contrast with findings from other foreland klippen in the central Himalaya. HMC rocks exposed in the Jajarkot klippe yield short‐lived, hairpin pressure–temperature–time–deformation paths that peaked at 550–600°C and 750–1,200 MPa at 25 Ma. The Main Central thrust (MCT) and the South Tibetan detachment (STD) bound the base and the top of the HMC, respectively, and were active simultaneously for at least part of their deformation history. The STD was active at c. 27–26 Ma and possibly as late as c. 19 Ma, while the MCT may have been active as early as 27 Ma and was still active at c. 22 Ma. The tectonometamorphic conditions in the Jajarkot klippe are characteristic of crustal thickening and footwall accretion of new material at the tip of the extruding metamorphic orogenic core. Our new results reveal that collisional processes active in the middle to late Miocene at the base of the HMC now exposed in the hinterland were also active earlier, during the Oligocene, at the tip of the southward‐extruding middle crust.

Age constraints on high-pressure/low-temperature metamorphism and sedimentation in the Luk Ulo Complex (Java, Indonesia)

Pre-Cenozoic blueschist- and eclogite-facies rocks occur widely scattered in the central Indonesian region, possibly representing lateral equivalents of the same subduction zone. High-pressure/low-temperature (HP/LT) metamorphism is thought to have occurred during the Early Cretaceous, which however is only constrained by K–Ar ages. This study is part of a systematic re-investigation of the regional geochronological record of various metamorphic rocks from this belt and focuses on the Luk Ulo Complex in central Java. Rubidium–Sr multipoint isochrons of one eclogite, two epidote-glaucophane schists and one epidote amphibolite yielded Early Cretaceous (Aptian) ages of 119–117 Ma (± 0.6–0.8 Ma). These ages are similar to previously reported K–Ar results, indicating that the existing data had not significantly been compromised by extraneous Ar contamination. Relatively low peak metamorphic temperatures (ca. 400 °C) during the HP/LT stage suggest that the Rb–Sr isotopic system was not significantly affected by diffusive loss during cooling. The Rb–Sr ages most likely constrain the time of mica growth or recrystallization during high-pressure metamorphism. The matching ages of high-pressure and lower pressure rocks are attributed to inheritance, but mixing of rocks that originally had formed at the same time at different depths of the subduction complex cannot completely be ruled out yet. Rubidium–Sr white mica ages of eclogite- and blueschist-facies rocks from central Java are younger than those of similar rocks from the Western Sulawesi tectonic province (130–120 Ma), revealing a previously unknown age difference that had been hidden by the poorer precision of the K–Ar dataset. At this point, it remains unclear whether this age difference is related to processes operating within the same or in different subduction zones.The zircon populations of clastic metasedimentary rocks from the Luk Ulo Complex are dominated by a prominent Jurassic to Carboniferous population (ca. 320–180 Ma) with a distinct Permo-Triassic peak (ca. 270–200 Ma). Another less pronounced Paleozoic age signal shows up at 450–380 Ma. Proterozoic and Archean zircon grains are very rare. At least some data points at the lower end of the age spectrum (ca.135–117 Ma) most likely are related to in-situ metamorphic processes. The youngest zircon grains of unambiguous detrital origin show up at ca. 160 Ma, indicating a Late Jurassic maximum depositional age. Additional detrital zircon data for the Barru Complex (Western Sulawesi) further substantiate previous findings documenting a complex age spectrum with contributions of Mesozoic (Triassic), Paleozoic (Permian, Carboniferous, Devonian to Ordovician), Meso- to Paleoproterozoic subpopulations and rare Archean zircons. The youngest zircons indicate a maximum depositional age of ca. 255–250 Ma. New and existing U–Pb zircon data indicate that the pre-metamorphic basin histories recorded in the Luk Ulo and Barru complexes are linked to different source terrains and depositional systems.

Crystallochemical indexes and geothermobarometric calculations as a multiproxy approach to P-T condition of the low-grade metamorphism: The case of the San Luis Formation, Eastern Sierras Pampeanas of Argentina

In this work, crystallochemical indexes and geothermobarometric calculations are used together to estimate the P-T condition in low-grade metamorphic units of the San Luis Formation from Sierra de San Luis (Eastern Sierras Pampeanas of Argentina). Phyllites and slates from this formation record at least two episodes of white mica (Wm) and chlorite (Chl) growth associated with main D1-S1 (Wm2-Chl1) and local D2-S2 (Wm3-Chl2) stages. Mean KICIS values of 0.30 (Western Belt) and 0.23 Δ°2θ (Eastern Belt) were determined for the <2 μm fraction. Moreover, since the average grain size of the Wm2 exceeds 10 μm, KICIS values were also measured for the 10–20 μm fraction ranging between 0.22 and 0.24 Δ°2θ for both belts. For those fractions, the KICIS values indicate epizone conditions, associated with temperatures higher than 300 °C. These values are comparable to temperatures obtained from chlorite thermometers, 316°–416 °C in Western Belt and 261°-403 °C in the Eastern Belt. Pressure values for D1 stage constrained from chlorite – white mica – quartz – H2O equilibrium are 2.5–5.1 kbar in the Western Belt, and at 3.3–4.7 kbar in Eastern Belt. The pressures are consistent with white mica b parameter values measured in samples from Western Belt (9.006 to 9.025 Å) and Eastern Belt (9.003 to 9.020 Å), linked to intermediate thermal gradients (25–35 °C/km).The identification of increasing P-T condition paths in low-grade metasedimentary successions is not easy in the absence of higher grade rocks; in these situations, a systematic sampling and analysis of dozens of samples must be carried out. The very good correlation between crystallochemical index values (Kübler index and white mica b parameter) and thermobarometric calculations (empirical and semi-empirical chlorite thermometers and thermobarometry for chlorite – white mica – quartz – H2O equilibrium) presented in this work argues in favor of the development of a multiproxy study strategy in this type of low-grade metasedimentary successions that involve: (1) a systematic sampling of metapelite levels for X-ray diffraction study (mineralogical and crystallochemical indexes with a rapid implementation allowing a dense systematic sampling); (2) the recognition of variations in the P-T conditions from KI and b parameter values and the consequent selection of metapelitic samples for analyzing mineral chemistry and thermobarometric calculations. In order to facilitate these calculations, a user-friendly spreadsheet for crystallochemical indexes and chlorite thermometry calculations is also provided.

Geochronology and Zr-in-rutile thermometry of high-pressure/low temperature metamorphic rocks from the Bantimala complex, SW Sulawesi, Indonesia

The timeframe of eclogite- and blueschist-facies metamophism in the central Indonesian region is poorly defined. Relative to its geographic extent, the regional coverage of isotopic age data is insufficient for an unambiguous interpretation of the geologic evolution of the Central Indonesian Accretionary Collision Complex. This study reports new geochronological constraints for high-pressure/low-temperature (HP/LT) rocks from the Bantimala Complex, SW Sulawesi, which further substantiate the importance of Cretaceous HP/LT metamorphism for the larger region. Multipoint Rb–Sr mineral isochrons of eclogites and glaucophane-rich rocks display a narrow range of white mica ages (130–120 Ma), interpreted to postdate peak-HP conditions, which is considerably smaller and more precise than the previously published K–Ar age spectrum (137–113 Ma). The close similarity with K–Ar ages suggests that these analyses were only slightly contaminated, if at all, with an extraneous Ar component, which did not significantly compromise the geological relevance of the existing dataset. An important result of this study is the emerging evidence for regional age differences between HP/LT rocks from SW Sulawesi (130–120 Ma) and Java (ca. 118 Ma). The existence of different subduction zones cannot be excluded but P–T and age differences between these occurrences can be reconciled with a model suggesting formation in the same subduction complex. Zircon is very rare in the studied HP/LT rock suite, but two glaucophane-rich rocks were suitable for U–Pb zircon dating and indicate Late Triassic–Early Jurassic protolith ages (ca. 205–185 Ma). The zircon population of a retrogressed eclogite records a more complex history including evidence for igneous crystallization, metamorphic recrystallization or growth, inheritance and variable degrees of Pb-loss. Metamorphic zircon rims mostly yielded U–Pb ages in the 135–110 Ma range that broadly confirm metamorphic ages determined by K–Ar and Rb–Sr white mica geochronology. Zircons that are significantly older (2.55–1.4 Ga and 400–260 Ma) than the protolith age are interpreted to represent detrital grains from subducted sediments that had been incorporated in mafic melts directly derived from a contaminated mantle source. The presence of continentally-derived detrital zircons that have presumably been included during melt formation in the mantle have not yet been described for any eclogite- and/or blueschist-facies rock of basaltic or gabbroic parentage.

Mineral footprints of the Paleoproterozoic sediment-hosted Abra Pb-Zn-Cu-Au deposit Capricorn Orogen, Western Australia

The minerals exploration undercover relies on the understanding of the ore-forming processes and the associated alteration characteristics that are used in vectoring towards a deposit. Previously, the proposed process for forming the 1590 Ma Abra base-metal deposit, hosted at 250 m depth in the Paleoproterozoic Edmund Basin of the Western Australian Capricorn Orogen, was through exhalation to the seafloor (SEDEX-style). Lacking any visible signs of alteration, sediments overlying the Abra deposit were perceived as younger, unaltered, and cutting the mineralisation and associated alteration comprised of siderite, chlorite and minor sericite. However, a recent study delineated a phengitic (i.e. Al-poor, Mg-, Fe-, Si-rich) white mica footprint in regolith above the deposit from hyperspectral field and remote sensing data. This study links the surficial mineral footprint to the deposit below through detailed analysis of hyperspectral data from drill core. The hyperspectral data processing results were validated using optical microscopy, micro-XRF and SEM-EDS analysis, and compared with geochemical, lithological and structural drill core data. Hyperspectral short-wave infrared (SWIR) data revealed a vertically zoned alteration footprint from the deposit to the surface, where very fine-crystalline phengitic white mica (i.e. sericite) and chlorite are most abundant a few tens of metres above the deposit. The abundance of chlorite gradually decreases, and the distal phengitic alteration is cut by the present erosional surface, but only moderately affected by weathering, confirming the surficial footprint detected in the previous study. Similarly, a vertically zoned carbonate alteration was delineated from thermal infrared (TIR) reflectance spectra from drill cores up to 2 km away from the deposit. Carbonate alteration from proximal to distal comprised of Mn-rich siderite, ankerite and ferroan dolomite, which replace the dolomite matrix in coarse-grained stratigraphic sequences. The replacement of dolomite matrix suggests that these permeable horizons acted as fluid conduits, which channelled hydrothermal fluids into sedimentary strata from a feeder structure. The presence of a vertically zoned carbonate and chlorite-phengite footprint in the overlying sediments advocates for their deposition before the ore formation at Abra, and a sub-seafloor replacement within a permeable sedimentary sequence as the ore-forming process. Comparable alteration footprints have been described around some world-class sediment-hosted base-metal deposits, including the Sullivan in the British Columbia, which is considered as a classic SEDEX-style by some and an exhalative-replacement hybrid by others. Also, identical footprints are common around the volcanic-hosted massive sulphide and are associated with the carbonate replacement-style deposits – an overlap which is an interesting future research space where hyperspectral technologies could provide answers. Validated hyperspectral data combined with geochemical, lithological and structural information enabled the identification of a subtle mineral footprint above the Abra deposit, and the established method can be used for vectoring towards other buried mineralisations – even through weathering.

Phyllic alteration and the implications of fluid composition at the Copper Flat hydrothermal System, New Mexico, USA

The Copper Flat hydrothermal system in Hillsboro, New Mexico, USA, is hosted by a partially brecciated porphyritic quartz monzonite intrusive body. Igneous rocks are alkaline to calc-alkaline, and chondrite-normalized rare earth element (REE) plots show enrichment in REEs that is consistent with other regional Laramide igneous rocks. Five assemblages of weak to moderate intensity phyllic alteration with distinct paragenetic relationships exist at the deposit and are classified as: early phyllic, quartz-sericite-pyrite (QSP), sericite-quartz, sericite-carbonate and late QSP. Carbonate is common and is part of some phyllic and the potassic alteration assemblages. Carbonates and phyllosilicates were analyzed by electron microprobe. White micas show substantial substitution of Al by Fe and Mg, and secondary biotite is Mg-rich. Relative to other porphyry Cu systems, the micas from Copper Flat contain, on average, greater F. Carbonates from veins and the replacement of mafic silicates and feldspars were determined to be mostly calcite, but reduced metal carbonates such as ankerite and rhodochrosite are also present in the alteration assemblages. The fluid(s) responsible for alteration are inferred to be CO2-rich and pH neutral as interpreted from the widespread presence of carbonates in both the potassic and phyllic alteration zones, and the white mica composition. Carbonate mineral compositions and absence of sulfates in the potassic alteration suggest that the hydrothermal fluids were not highly oxidized and were sulfur-poor. These features of alteration and geochemistry at Copper Flat are atypical of most porphyry Cu-Mo deposits in the southwestern U.S. and may be more characteristic of porphyry Cu-Au and porphyry Mo deposits.

The Jurassic tourmaline–garnet–beryl semi-gemstone province in the Sanandaj–Sirjan Zone, western Iran

ABSTRACT Deposits of semi-gemstones tourmaline, beryl, and garnet associated with Jurassic granites are found in the northern Sanandaj–Sirjan Zone (SaSZ) of western Iran, defining a belt that can be traced for about 400 km. Granitic magmas strongly interacted with or were derived from melts of continental crust and/or sediments. Based on morphologies, size, mineral assemblage, and contact relationships with host granite and associated metamorphic aureoles, these deposits are categorized into six types: (1) garnet in skarns, (2) tourmaline, beryl, and garnet in pegmatite and aplitic dikes, (3) disseminations and patches of tourmaline in leucogranites, (4) quartz-tourmaline veins in granite, (5) tourmaline and garnet in metamorphic aureoles, and (6) tourmaline orbicules in aplite. Tourmalines are mostly schorl and dravite, and garnets are mostly almandine, spessartine, and grossular. Tourmaline, beryl, and garnet from pegmatites in the contact aureole of Jurassic granites reflect segregations of Be, B, Mn, and Al bearing melts from the Jurassic peraluminous granites. Quartz-tourmaline veins and hydrothermal garnets in skarns reflect fluids exsolved from the surrounding metasediment and pegmatite melt. In contrast, tourmaline patches and orbicules developed from boron-rich aqueous fluids exsolved from cooling granitic magma. Distribution of semi-gemstones in the SaSZ shows that these are mostly related to pegmatites associated with Jurassic granitic intrusions. Mineral equilibrium considerations indicate that SaSZ semi-gemstones crystallized at P = 3.5–7.5 kbar (11.5–25 km deep) and temperatures of 550–650°C. SaSZ pegmatites fall in the muscovite (MS) and MS-rare element classes. They are Lithium Cesium Tantalum (LCT)-type pegmatites. Fluids responsible for gem mineralization were exsolved from cooling granite bodies and released by metamorphosed sediments. Further studies are needed to better understand the northern Sanandaj–Sirjan tourmaline–garnet–beryl semi-gemstone Province.