Eclogite-like rocks from Southern Pirin Mountains – preliminary results about petrology and time of formation

North-northeast of the village of Ilinden (Southern Pirin Mnt.) three eclogite boudins were separated on the geological map in scale 1:50 000 (Sarov, 2010). The rocks belong to the Slasten lithotectonic unit. The mineral assemblage and mineral chemistry do not allow these rocks to be classified as eclogites. They can be considered as eclogite-like ones, formed by postmagmatic-metasomatic alteration of the host rocks. Based on LA-ICP-MS sphene U-Pb dating, eclogite-like rocks yield a Late Jurassic age (160±19 Ma).

FORECASTING GEOCHEMICAL PREREQUISITES FOR DETECTING THE PORPHYROUS SYSTEM IN THE KOMSOMOLSK REGION OF KHABAROVSK REGION

The information on the results of geological exploration work to identify the porphyry system in the Komsomolsk region of the Khabarovsk Territory is given. It is shown that copper-molybdenum-porphyry mineralization is associated with the type of porphyry deposits by a porphyry stock surrounded by fields of hydrothermal-metasomatic alteration. The possibilities of the object of the gold-rare metal type are substantiated.

REE minerály fenitů čistecko-jesenického masivu (Česká republika)

Alkaline metasomatites (fenites) originated by pervasive Na metasomatism of granitoids of the Čistá-Jesenice Pluton (belonging to the Teplá-Barrandian unit in the NW part of the Bohemian Massif) contain a rich association of REE-bearing minerals. The occurrence of REE carbonates (bastnäsite, parisite), monazite, rhabdophane, churchite, fergusonite and pyrochlore was found in relatively weakly altered rocks (typical fenites), whereas much richer assemblage was observed in rocks which underwent the strongest metasomatism (so called reomorphic cancrinite-nepheline syenites). Here, the mineral assemblage includes in addition to all above mentioned minerals also xenotime and REE silicates, including tritomite/melanocerite, allanite, perbøeite, gadolinite and a Mn-analogue of hingganite. A common mineral phase is zircon in these rocks, too. Cerium, yttrium, and to lesser extent also lanthanum are dominating cations in the studied REE phases. A total of 24 mineral species was identified, including three unnamed phases. In most of the studied phases, the level of fractionation of REEs is high, exceptionally even extreme. Chondrite-normalized REE patterns of some phases are characterized by a pronounced M-type tetrad effect. The results of microprobe analyses suggest that individual minerals originated during several episodes, characterized by different chemical composition of the mineral-forming medium (especially with contrasting concentrations of strong REE-complexing ligands and oxygen fugacity) and/or temperature. We did not find any significant differences in chemistry of individual minerals present in various rock types showing different levels of metasomatic alteration. The obtained data are consistent with hydrothermal origin of most (if not all) reported REE-bearing phases. The material source and genesis of the studied REE+Nb+Zr mineralization was in all probability associated with hydrothermal activity in the exocontact of a deep-seated hypothetical carbonatite intrusion, as was suggested already in earlier works dealing with these remarkable rocks.

Listvenites: new insights of a hydrothermal system fossilized in Cerro Matoso peridotites, Montelíbano, Córdoba Department, Colombia

The products of metasomatic alteration (e.g., carbonation) of peridotites are called listvenites. Based on a description of the outcrops in the laterite deposit at Cerro Matoso located in the NW of Colombia, the mineralogical composition confirmed by petrography, and a chemical analysis performed with XRF and WDS/EDS, the previous unit called tachylite is redefined as listvenite. Two types of listvenites are described: listvenite A, with the mineralogical association of quartz + siderite + phyllosilicates + goethite +/- magnetite, and listvenite B, with the association of siderite + phyllosilicates + goethite. Cr-spinel relics accompanied by Mn-siderite and neoblastic textures, indicate their origin from peridotites, where Mn-Fe would have been deposited by hydrothermal fluids. Hydrothermal reducing environments with alkaline fluids and low temperatures should have favored the formation of listvenites that are observed along a fracture zone, oriented WNW-ESE at Pit-1 in Cerro Matoso. Due to exposure to climatic conditions since the Eocene, but definitively since the last Andean Orogeny, listvenites were affected, like all the rocks in the Cerro Matoso deposit, by intense supergene weathering and leaching processes, which could make their true origin unclear.

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.

Mineralogy and Fluid Regime of Formation of the REE-Late-Stage Hydrothermal Mineralization of Petyayan-Vara Carbonatites (Vuoriyarvi, Kola Region, NW Russia)

The Vuoriyarvi Devonian alkaline–ultramafic complex (northwest Russia) contains magnesiocarbonatites with rare earth mineralization localized in the Petyayan-Vara area. High concentrations of rare earth elements are found in two types of these rocks: (a) ancylite-dominant magnesiocarbonatites with ancylite–baryte–strontianite–calcite–quartz (±late Ca–Fe–Mg carbonates) ore assemblage, i.e., “ancylite ores”; (b) breccias of magnesiocarbonatites with a quartz–bastnäsite matrix (±late Ca–Fe–Mg carbonates), i.e., “bastnäsite ores.” We studied fluid inclusions in quartz and late-stage Ca–Fe–Mg carbonates from these ore assemblages. Fluid inclusion data show that ore-related mineralization was formed in several stages. We propose the following TX evolution scheme for ore-related processes: (1) the formation of ancylite ores began under the influence of highly concentrated (>50 wt.%) sulphate fluids (with thenardite and anhydrite predominant in the daughter phases of inclusions) at a temperature above300–350 °C; (2) the completion of the formation of ancylite ores and their auto-metasomatic alteration occurred under the influence of concentrated (40–45 wt.%) carbonate fluids (shortite and synchysite–Ce in fluid inclusions) at a temperature above 250–275 °C; (3) bastnäsite ores deposited from low-concentrated (20–30 wt.%) hydrocarbonate–chloride fluids (halite, nahcolite, and/or gaylussite in fluid inclusions) at a temperature of 190–250 °C or higher. Later hydrothermal mineralization was related to the low-concentration hydrocarbonate–chloride fluids (<15 wt.% NaCl-equ.) at 150–200 °C. The presented data show the specific features of the mineral and fluid evolution of ore-related late-stage hydrothermal rare earth element (REE) mineralization of the Vuoriyarvi alkaline–ultramafic complex.

Rare-earth accessories and secondary minerals in plagiogneisses from the Stankuvatske Li-deposite

The Stankuvatske Li deposit (SD) is situated at western flank of the Lypniazka structure (Ingul megablock of the Ukrainian Shield). Knowledge about REE content in host metamorphic rocks is based on the results of bulk chemical analysis, but their minerals have not been determined. For the first time rare-earth mineralization of the Stankuvatsky lithium deposit has been investigated in fine-grained gneiss with «augen» and schistose structure, porphiroblastic texture, formed as result of tectonical alteration. Our investigations were carried out using petrographic and microprobe analysis (EPMA). Mineralogically gneisses consist of quartz, plagioclase, zoizite, biotite, graphite, chlorite and abundant sulphides mainly represented by pyrite, arsenopyrite, sphalerite, molibdenite. Accessory minerals presented by titanite, apatite, monazite, zircon and coffinite. Gneisses have been subjected to deformation and hydrothermal — metasomatic alteration. An investigation of rock-forming and accessory minerals allows to revel low-temperature alterations of primary allanite by bastnäsiteand chlorite with formation of secondary bastnäsite-chlorite-coisite-pyrite association with «coronary» texture. The penetration of S, F, CO2, H2O enriched fluids were caused disintegration, partial redistribution and reprecipitation of rare earth elements. As result synhysite-chlorite-pyrite association was formed.