Ore deposits

Pb-Zn barite, celestite, florite, celestobarite, fluorite Ore Deposits in Tunisia (North Africa) , Jurassic, Cretcaceous, Triassic Salt diapris
Jebel El Kohol, Jebel Stah, Jebel Mecella, Hammam Zriba, Jebel Guebli, Fedj el Adoum, Fej Lahdoum, Bou Jaber, Fluid inclusion stable isotopes (sulphur, carbon, oxygen) Metallogeneis

SULFUR SPRINGS IN THE “GRUPPI DI VOLTRI” OPHIOLITE COMPLEX (ITALY)

The Voltri Group is an Alpine-type ophiolite complex, which have been affected by the Alpine orogenesis and the consequent metamorphism, that completely canceled  the stratigraphic relationships and gave rise to important green schist facies modifications which often make it difficult to recognize the original nature of the rocks.  The most important forming lithotypes are: lherzolites, serpentintinites, metagabbros, prasinites, amphibolites, quartzites, shales: acid crystalline schists are present along the western margin.

Metallic oxides and sulphides are scattered in all lithotypes and locally form discrete massive bodies, such as concentrations of pyrite and chalcopyrite, with other sulphides and sulphosals, in prasinitic rocks and in contact between these and calcescists. However, the most interesting mineralizations are the hydrothermal quartz veins in alterated serpentinites, that form small deposits know in ancient Italian literature as “ydrothermalites”, to day better know as “listwaenites”, or “listvenite” and similar, derived from Russian word.  These are stock-work type deposits, mainly composed by quartz and Ca-Mg carbonates with gold, pyrite, chalcopyrite, galena, sphalerite, tetrahedrite, pyrrhotite, and nickel sulphides, cementing crushed breccias near the contact between ultramafics and metabasites, or cutting serpentinites near the above contact. 

The presence of a few sulfur springs was known, many others have been identified by the author, and have been analyzed in order to study the relationship with the mineralizations genesis. In particular, the H2S content was analyzed at the source, with the innovative method of  GOLTELMAN (1974), in the laboratory the contents of the main elements were then analyzed.  All such springs show very similar chemistry; they are medio-mineral  type, and can be comprised in a family of sulfur-alkaline springs on the basis of  their dissolved substances. Some hydrogeological and geochemical conjectures on the origin of the springs, with particular  regard  to  the  H2S,  are  proposed.  The  formation of this one is not attributed  to biogenic  processes,  but  to  chemical  reactions  promoted by the abundance of metalliferous sulfides.

Another sulfur spring, flowing out from cenozoic sediments very close to the Voltri Group, shows different  chemistry and  can  be  comprised  in  a family  of  sulfate-alkaline  earth springs.

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This volume records the proceedings of a conference held at the University of New England in November 2010 that follows on a tradition of New England geology symposiums held in 1982, 1988, 1993 and 1999. It has been 10 years since the last symposium. This volume is split into themes covering I) Tectonics; II) Alumi; III) Granites; and IV) Mineralisation.

This proceedings volume honours the lifelong works of Professor Peter Flood, Professor Bruce Chappell and Professor Paul Ashley for their contributions to tectonics, granites and mineralization respectively in the New England Orogen.

The committee members comprise: Solomon Buckman, Peter Flood, Phil Blevin, Bruce Chappell, Jonathan Aitchison, Paul Ashley, John Patterson, Mel Jones.

Copyright is retained by the first or sole author, who grants right of first publication to the NEO 2010 Conference Proceedings.

Permission is granted to distribute this article for nonprofit, educational purposes if it is copied in its entirety and the Conference Proceedings is credited.

ISBN  978 1 921597 24 4

Reservoir-infiltration uranium deposits («sandstone» type) today are the main active source of
uranium mineral raw materials in the world and the only one in Kazakhstan. Their main advantage in the form of
better environmental friendliness, productivity and minimum production costs creates prospects for their further
detection in various parts of the world. It is important to simplify and improve multi-stage, expensive and difficult
geological exploration works for the purpose of forecasting and searching them with affordable innovative solutions.
The available multispectral satellite imagery has opened up new opportunities for the study of uranium ore
provinces. Mapping of uranium ore provinces based on multispectral satellite imagery allows them to be compared
with certain key ore-controlling data from geological and geophysical studies. The near-surface visible nature of
geotectonic structures, climatic conditions and zonal anomalies are more easily and efficiently visualized using
modern space technologies and computer solutions. The explanation of the derived correlations with the geotectonic
and climatic conditions allows the use of multispectral images in order to simplify and improve the quality of
forecasting, prospecting and exploration of reservoir-infiltration uranium deposits. More advanced aerial and space
remote sensing methods make it possible to detect surface anomalies associated with this type of ore. The scientific
explanation of the nature of these anomalies and their role in the geological and genetic model of ore formation
creates a solid theoretical basis for improving the exploration methodology. The convergence of the results obtained,
their theoretical explanation, simplicity and convincingness of the results make it possible to make new predictions
of promising areas of reservoir-infiltration uranium regions for several of the key ore-controlling factors and use this
methodology in conjunction with other data from regional and local studies at all stages of exploration

The Belessa kaolin deposit in the western margin of the Central Main Ethiopian Rift was studied using geological, mineralogical, chemical and physical methods to understand its genesis and evaluate its potential suitability for different industrial applications. X-ray diffraction and Scanning Electron Microscopy were used to establish the mineralogical composition. Bulk chemical compositions were determined using ICP-MS and ICP-AES. The geology of the kaolin district is comprised of Miocene to Quaternary age rhyolite and pyroclastic tuff. The kaolin occurrence is located in the central part of the study area and is associated with rhyolite. The host rock is composed of quartz and alkali feldspar phenocrsyts set in a groundmass of very fine grained quartz, alkali-feldspar and plagioclase. The rhyolite is partially to completely altered to kaolin. The kaolin deposit is composed predominantly of kaolinite and quartz. The kaolinite minerals of the deposit have high structural order. The geological, mineralogical and geochemical studies indicate that supergene alteration played a major role in the formation of the Belessa kaolin deposit. The absence of quartz veining and alteration zones containing high temperature minerals precludes significant hypogene alteration. The Chemical Index of Alteration (CIA) and Chemical Index of Weathering (CIW) also show that the host rock experienced strong alteration and weathering. Furthermore, high Ce+Y+La values correspond to supergene-type alteration. The low P and high Cr+Nb concentrations also support a supergene origin. The physical properties, chemistry, mineralogy and crystal morphology indicate that the Belessa kaolin has potential applications for paper coating, filler (in paper, rubber, plastic and paint), ceramics, pharmaceuticals and cosmetics.

Bolivia cubre en la parte oriental una región con una superficie de 220,000 km2 que corresponde a una pequeña parte del gran cratón Amazónico con afloramientos de rocas Meso-Proterozoicas (1.8-1.0 Ga). Aproximadamente diez por ciento de este regolito consiste de “esquistos” de metamorfismo bajo a medio. Investigaciones de los últimos veinticinco años demostraron que estos se presentan en Guarayos y la Chiquitania con características de cinturones de rocas verdes con potencial geológico importante para depósitos de oro orogénico y yacimientos de sulfuros masivos volcanogénicos (VMS). En este contexto el descubrimiento del depósito VMS “Miguela” hace veinte años representa un hallazgo bastante importante en la exploración minera del oriente Boliviano. Está hospedado en una secuencia volcano-sedimentar con afinidad toleítica dentro del cinturón de rocas verdes de Guarayos. Los estudios regionales del pasado no tomaron en cuenta la búsqueda sistemática para este tipo de depósitos, tampoco la aplicación de métodos innovadores de exploración para permitir el descubrimiento de cuerpos mineralizados que no afloran y no dejan rasgos en superficie. Los sulfuros masivos de “Miguela” están ligados a la formación “La Pastora”, que se extiende sobre una distancia de por lo menos doce kilómetros. Los tres lentes mineralizados son ricos en cobre y oro. La mineralización se formó como precipitación submarina e impregnación dentro de los sedimentos y rocas volcánicas con un control por una falla sin-volcánica.

Banded Iron Formations (BIFs), as the name suggests, are chemically precipitated sedimentary rocks having alternating Fe-rich and Si-rich bands. The origin of BIF has always remained a debated topic of research. The BIF in the Badampahar Greenstone Belt is of Mesoarchean age that formed a part of the East Indian Shield. Here, the BIF is interlayered with metavolcanic rocks, quartzite, phyllite, and chert, which indicates a typical greenstone sequence. The present paper focuses a little on the depositional setting of the BIF and mostly on the post-depositional processes, which include formation of iron ores. Geochemical and sedimentological evidences suggest insignificant detrital input in the genesis of BIF and significant chemical precipitation in the deposition. The post-depositional processes involved subsequent stages of deformation, metamorphism, hydrothermal, and supergene processes after deposition. Hydrothermal fluid is found enriched in High Field Strength Elements (HFSEs) and transition elements. This hydrothermal fluid altered the BIF to form titanomagnetite and ilmenite-rich rock in Jashipur. Recycling of BIF magnetite into hematite and removal of silica also attributed to hydrothermal alteration, which ultimately led to form iron ores.

Los depósitos de pórfido ricos en oro en todo el mundo se adaptan bien a un modelo descriptivo generalizado. Este modelo incorpora seis facies principales de alteración hidrotermal y mineralización, las cuales son zonificadas hacia arriba y hacia afuera con respecto al stock del pórfido compuesto de forma cilíndrica encima de los plutones parentales mucho más grandes. Este ambiente intrusivo y su lithocap argílica avanzada superpuesta se extiende aproximadamente 4km verticalmente, un intervalo sobre el cual se observan cambios profundos en el estilo y mineralogía del oro y la mineralización de cobre asociada.

Porphyry copper deposits result from the complex interactions and feedbacks of many processes. Owing to the complexity, a succinct definition that includes the essential attributes of this deposit class is elusive. Consequently, this descriptive model uses a working definition of a porphyry copper deposit. A porphyry copper deposit is
1. One wherein copper-bearing sulfides are localized in a network of fracture-controlled stockwork veinlets and as disseminated grains in the adjacent altered rock matrix;
2. Alteration and ore mineralization at 1-4 km depth are genetically related to magma reservoirs emplaced into the shallow crust (6-8+ km), predominantly intermediate to silicic in composition, in magmatic arcs above subduction zones;
3. Intrusive rock complexes that are emplaced immediately before porphyry deposit formation and that host the deposits are predominantly in the form of upright vertical cylindrical stocks and/or complexes of dikes;
4. Zones of phyllic-argillic and marginal propylitic alteration overlapping and surrounding a potassic alteration assemblage; and,
5. Copper may also be introduced during overprinting phyllic-argillic alteration events.

The extractive industries (EI) sector occupies an outsize space in the economies of many developing countries. Economists, public finance professionals, and policy makers working in such countries are frequently confronted with issues that require an in-depth understanding of the sector. The objective of this volume is to provide a concise overview of EI-related topics these professionals are likely to encounter. The volume provides an overview of issues central to EI economics; discusses key components of the sector’s governance, policy, and institutional frameworks; and identifies the public sector’s EI-related financing obligations. Its discussion of EI economics covers the valuation of subsoil assets, the economic interpretation of ore, and the structure of energy and mineral markets. The volume maps the responsibilities of relevant government entities and outlines the characteristics of the EI sector’s legal and regulatory frameworks. Specific key functions of the sector are briefly discussed, as are the financial structures that underpin environmental and social safeguards; investment of public revenues generated from oil, gas, or minerals; as well as extractive-based economic diversification. The authors hope that decision makers in ministries of finance, international organizations, and other relevant entities will find the study useful to their understanding and analysis of the EI sector.

Framboids, spherical aggregates of minute, usually pyrite, grains are the commonest texture of sulfides in sedimentary rocks. They also occur in many other environments, ranging from magmatic rocks to antiquarian books. Framboidal textures are formed by several minerals including copper and zinc sulfides, greigite, magnetite, magnesioferrite or hematite, as the products of both primary deposition and replacement. Special attention is paid to pyrite framboids in this paper, with detailed descriptions of different framboid-related forms: annular framboids, sunflower framboids, micro- and polyframboids. Framboidal forms are often hierarchically structured over three size scales, with complexities ranging from microframboids, to framboids, and to polyframboids. Pyrite in framboids results from inorganic reactions between dissolved iron and sulfide, with a greigite intermediary. The sulfur is usually biogenic in origin. Simple pyrite framboids are formed during aggregation, possibly enhanced by the magnetic properties of the monosulfide precursor. Further processes, including particulation and organically controlled aggregation, result in more complicated forms such as polyframboids. Pyrite framboids can grow to euhedral grains provided the supply of iron and sulfide is not limited. Pyrite framboids often occur in close spatial relationship with organic matter, silica or carbonates, which influence their formation and growth. Replacement of iron sulfide framboid-related forms by other minerals can be indicative of sediment diagenetic conditions, or additional processes such as mineralization in ore deposits. Framboids influence the distribution of many trace elements. Due to their high specific surface areas, framboids can accumulate these trace elements during growth. Recrystallization of framboids can redistribute many trace elements. An overview of the common association between pyrite framboids and fossils is given, stressing both the importance of organic matter in framboid formation, and of the framboids in the processes of mineralization and preservation of fossils. Iron sulfide framboids may have influenced the earliest stages of life formation on the Earth as a source of energy and catalytic action, by accumulating organic compounds, and by acting as reaction chambers and templates which facilitated reproduction and information transfer. Applications from framboid studies are presented, ranging from determination of the redox conditions in water and sediment columns using size and distribution of framboids, to evaluation of deterioration processes in museum specimens.

In the northern part of the Bahariya Depression (Western Desert, Egypt) the Eocene carbonate succession , unconformably overlying the Cretaceous deposits, consists of three main stratigraphic units; the Naqb, Qazzun and El Hamra formations. The Eocene carbonates are relevant as they locally host a large economic iron mineralization. This work revises the stratigraphic attribution of the Eocene formations on the basis of larger benthic foraminifers from both carbonate and ironstone beds. Eight Nummulites species spanning the late Ypresian e early Bartonian (SBZ12 to SBZ17) were identified, thus refining the chronostratigraphic framework of the Eocene in that region of Central Egypt. Moreover, additional sedimentological insight of the Eocene carbonate rocks is presented. The carbonate deposits mainly represent shallow marine facies characteristic of inner to mid ramp settings; though deposits interpreted as intertidal to supratidal are locally recognized. Dating of Nummulites assemblages from the youngest ironstone beds in the mines as early Bartonian provides crucial information on the timing of the hydrothermal and meteoric water processes resulting in the formation of the iron ore mineralization. The new data strongly support a post-depositional, structurally-controlled formation model for the ironstone mineralization of the Bahariya Depression.

Over one hundred samples, representing mainly clayey-organic- and carbonate-rich shales (Kupferschiefer)
but also other members of different ore sections, including hangingwall dolomites (Z1 Werra) and footwall
Weissliegend sandstone (Lower Permian), have been collected in differentmines of the Lubin–Głogówmining district,
mainly near the contact (transitional zone) between the copper-mineralized zone and secondarily oxidized
(Rote Fäule = RF) zone. In general, the Polish Kupferschiefer shales are enriched in MREE in comparison to
NASC. In a typical copper-rich ore section the REE amounts and patterns depend on lithologies, being generally
similar in shales and dolomite. ΣREE vary among sandstones, shales and dolomites (average 73, 143 and
85 ppm, respectively), probably reflecting mainly their clay contents. Sandstones have strongly convex REE
patterns with positive Eu and negative Gd anomalies and depletion in LREE and enrichment in MREE relative
to HREE. The REE patterns of shale and dolomite are similar to one another and rather flat, with strong negative
Eu anomalies, and a small positive Gd anomaly in the case of shales.
The REE patterns of shales from the mineralized Cu-zone are generally convex (MREE enriched) and have
negative Eu anomalies. However, in a section with Cu-, Zn- and Pb-shales the REE pattern of Pb-bearing
shales shows a positive Eu anomaly, in contrast to other shales and overlying dolomite. More oxidizing
conditions of deposition can be assumed for Pb-shales.
No significant differences between REE distributions in transitional and oxidized zones have been observed.
Their REE patterns are more convex and are much higher (av. 247 ppm) than those in the mineralized zone
and they do not show Eu anomalies. The strongly convex pattern may suggest either enrichment in MREE
or relative depletion in LREE due to localized precipitation of light REE minerals, both in shales and in the
uppermost part of the sandstones.
Two unique sections, one Cu-rich and one Cu-lean (partly oxidized), comprising three shale beds interbedded
with dolomites have been compared. Generally ΣREE contents are similar in these two sections. Also similar
are changes in contents of REE between beds in both sections, which decrease significantly upwards (from
157–171 ppm to 54–60 ppm). The REE patterns of the lowermost beds (directly overlying sandstones) are
ramp-like, with LREE enrichments. The upper beds have concave REE patterns. Comparison between sections
shows generally stronger negative Eu and positive Gd anomalies in the highly-mineralized section.
There is a highly significant positive relationship between Cu and ΣREE contents in Cu-rich shales and
slightly less significant negative relationship for their concentration in oxidized and transitional shales.
There is a moderate significant positive correlation between P2O5 andΣREE contents in Cu-rich shales.
The observed differences in REE contents cannot be provenance dependent but have been caused by diagenetic
processes, possibly related to mineralization and oxidation processes. Europium anomalies, generally reflecting
different Eh conditions in the deposit, can be eliminated by the prolonged oxidation. Strong enrichment of the RF
zones in REE may result fromtheir desorption fromlarge volumes of oxidizing, includingmineralizing, solutions
which probably emerged from the underlying molasse lithologies into the Rote Fäule areas. Higher contents
of REE in the lowermost shales suggest upward movement of solutions from the underlying sandstones also
far away from the RF areas.

The Kletno deposit in the Śnieżnik Massif (Central Sudetes, SW Poland), mined for Fe, U, Ag, Cu, fluorite, and marble through the ages, developed at the contact of marbles and orthogneiss. Here, we present a new Fe-Ti-V-ore (containing up to 14.07 wt.% Fe, 2.05 wt.% Ti, and 2055 ppm V in bulk rock) and ornamental- to gem-quality talc prospect at the southwest margin of this deposit. This newly documented Fe-Ti-V mineralization is hosted in hornblendites, dolomite veins, and chlorite schists, which, along with talc, envelopes a tectonic slice of serpentinite. Hornblendites are interpreted as metamorphosed ferrogabbros, derived from the same mafic melts as adjacent barren metagabbros. The oxygen and carbon isotope compositions of metabasites and dolomite veins (amphibole δ18O values = 8.8-9.3‰; carbonate δ18O values = 12.8-16.0‰, and δ13C values = −8.3‰ to −7.2‰), in combination with those of the country marbles (carbonate δ18O and δ13C values = 23.2‰ and +0.1‰, respectively), suggest that mineralization-bearing hornblendites formed due to interaction of the mafic magma with CO2 released during the decarbonation of the sediments. The CO2-bearing fluid interaction with gabbros likely caused carbonation of the gabbros and formation of the dolomite veins, whereas talc formed due to Si-rich fluids, possibly derived from a mafic intrusion, interaction with serpentinite, or due to the metasomatism of the serpentinite-gabbro assemblage. Moreover, fluids leaching Fe and Ti from the adjacent sediments can mix with the mafic magma causing enrichment of the magma in Fe and Ti. Consequently, the mineralization-bearing ferrogabbros became even more enriched in Fe and Ti, which can be linked with the formation of Fe-Ti-V ore bodies.

Breccia are key elements of the polymetallic iron oxide copper-gold (Co-Ag-Bi-U) (IOCG) deposits worldwide. Their use is however difficult either in regional mineral exploration or in production mapping. Recent studies on breccias in magmatic-hydrothermal systems show that genetic information may be determine from quantitative geometric parameters (shape and spatial organization of fragments) and composition. Breccia maturity could be determined from several parameters et could be use for targeting mineralization. In IOGC(U) ore deposits, breccias occurs in all geological environments and at different depths. Corroded breccia fragments and chaotic particle size distribution are more abundant than in other types of ore deposits, underlying the role of solution process in this class of deposits. Résumé Les brèches sont des éléments essentiels dans les gisements d'oxydes de fer polymétalliques à cuivre-or (Co-Ag-Bi-U). Leur utilisation reste cependant difficile, aussi bien en exploration régionale que lors de la cartographie au cours de la production. Les études récentes sur les brèches dans les systèmes magmatiques-hydrothermaux ont montré qu'il était possible d'obtenir de multiples informations génétiques à partir d'analyses géométriques détaillées sur la forme et l'organisation spatiale des fragments en tenant compte de la composition. La maturité d'une brèche peut se mesurer selon différents paramètres et peut servir de vecteur vers la minéralisation. Dans les gisements IOGC(U), les brèches apparaissent dans tous les environnements et à diverses profondeurs. Les fragments des brèches sont plus corrodés et la granulométrie est plus chaotique que dans d'autres types de gisements, ce qui souligne l'importance des processus de dissolution dans ces gisements.

A desktop study and geological analysis on current Wetar Project datasets were carried out to establish certain key criteria which related to the volcanic massive sulphide mineralization processes and the deposition of economic resources in the Wetar mineralization district. The primary objective is to identify deposit-scale exploration targets with potential to be developed into mineable copper and/or gold reserves within Batutua’s tenements at Wetar Island.

The first stage of the study is the identification of regional tectonic scale structures that may concentrate the flow of fluids (magma and metal-bearing fluids). The intersection of structural zones, characterized by inverted rifts, defines the prospective mineralization belts and determines camp-scale and deposit-scale targets.

Camp-scale and deposit-scale targeting involves analyses and interpretation of more detailed geological and structural datasets, together with geophysical and mineral occurrence data to define specific areas of exploration potential.

All targets are ranked on a technical basis utilizing ASC criteria and a simple numerical scoring scheme. Key criteria comprise favorable geological setting including specific host rocks, uplift and erosion rates, prospect scale faulting, post-mineral cover and mineral occurrences or alteration assemblages. 

Keyword: Area Selection Criteria (ASC), Wetar mineralization district, volcanic massive sulphide (VMS), camp-scale target, deposit-scale target

It has been suggested that the two morphologies
of sedimentary pyrite, framboids and euhedra, may
reflect two distinct pathways of pyrite formation. Framboids
form indirectly via iron monosulphides, whereas
euhedra form from direct precipitation from solution.
A third pathway which is bridging these two forms is
proposed here, namely the continuous growth from
a monosulphide globule through framboids to a euhedral
single crystal. It is also suggested that framboids probably
occur over a range of three orders of magnitude, from the
least complex microframboids through framboids to
polyframboids.

Abstract: Base, rare and precious metal deposits are widespread in the Caucasus and Pontides regions.
They are the result of the Phanerozoic evolution of the Tethys Ocean, of various geodynamic settings,
including oceanic, intra-arc, back-arc and island arcs. The various types of mineralization are discussed
in terms of the participation scale of sialic, basaltic crusts and mantle sources. In oceanic settings, cupriferous
Cyprus-type deposits occur, where the source of Cu is the mantle. In intra-arc settings, Beshi type
Cu-Zn deposits were formed; the source of Zn is interpreted to be basaltic crust. As for the island arc
and back-arc settings, Cu-Pb-Zn porphyry, stockwork, VMS and vein deposits are common. The source
of Pb is interpreted to be the sialic crust. The rare metals (Hg, W, Sb) are related to post-collisional settings,
where sialic crust is important. Mo is also related mainly to post-collisional settings, and it subordinately
participates in the island arc settings. Precious metal mineralization (Au and Ag) predominantly
developed in island arc and post-collisional settings. Therefore, in the process of mantle depletion and
crust formation precious metals (Au and Ag) mainly accumulated in the sialic crust.

The present study focuses on the kaolin deposit in Kalabsha area south Western Desert of Egypt in an attempt to determine its possible source, tectonic setting, and weathering history by means of integrated petrographical and geochemical approaches. The petrographical study was worked by microscopic investigation and supported by X-ray diffraction analysis. X-ray fluorescence and inductively coupled plasma-mass spectrophotometry methods were used for the determination of the bulk elemental composition. Mineralogical analysis revealed that kaolinite is the main clay mineral component indicating a severe chemical weathering of Al-rich source rocks and complete leaching under warm, semiarid climatic conditions. The nonclay minerals are represented by quartz, iron oxides and hydroxides, Ti-bearing minerals, and zircon. Geochemical data show a prevalence of SiO 2 and Al 2 O 3 and enrichment of Hf, Nb, Ta, Th, U, and Zr that support the kaolinitic nature of the deposits and their derivation from a felsic granitic terrain. The high values of the chemical index of alteration and the lower values of the index of compositional variability also suggest an intensive weathered source area and the geochemical maturity of the sediments. Other relevant geochemical discriminant functions and plots reveal felsic igneous parent rock for the kaolin deposits. Q-mode hierarchical cluster analysis combined with the normalized rare earth element patterns played a crucial role in unraveling the origin of the studied deposits. The results show that the most probable source rock of the Kalabsha kaolin deposits is the intense weathering of relatively proximal Adara Adatalob granites and their similar rock types in the Arabian-Nubian Shield from the south Eastern Desert of Egypt.

Corundum (ruby-sapphire) is known to have formed in situ within Archean metamorphic rocks at several localities in the North Atlantic Craton of Greenland. Here we present two case studies for such occurrences: (1) Maniitsoq region (Kangerdluarssuk), where kyanite paragneiss hosts ruby corundum, and (2) Nuuk region (Storø), where sillimanite gneiss hosts ruby corundum. At both occurrences, ultramafic rocks (amphibole-peridotite) are in direct contact with the ruby-bearing zones, which have been transformed to mica schist by metasomatic reactions. The bulk-rock geochemistry of the ruby-bearing rocks is consistent with significant depletion of SiO2 in combination with addition of Al2O3 , MgO, K2O, Th and Sr relative to an assumed aluminous precursor metapelite. Phase equilibria modelling supports ruby genesis from the breakdown of sillimanite and kyanite at elevated temperatures due to the removal of SiO2. The juxtaposition of relatively silica-and aluminum-rich metasedimentary rocks with low silica ultramafic rocks established a chemical potential gradient that leached/mobilized SiO2 allowing corundum to stabilize in the former rocks. Furthermore, addition of Al2O3 via a metasomatic reaction is required, because Al/Ti is fractionated between the aluminous precursor metapelites and the resulting corundum-bearing mica schist. We propose that Al was mobilized either by complexation with hy-droxide at alkaline conditions, or that Al was transported as K-Al-Si-O polymers at deep crustal levels. The three main exploration vectors for corundum within Archean greenstone belts are: (1) amphibolite-to granulite-facies metamorphic conditions, (2) the juxtaposition of ultramafic rocks and aluminous metapelite, and (3) mica-rich reactions zones at their interface.

The Kambale graphite deposit is located within the Wa Lawra ‐ greenstone belt in NW Ghana. Historical records, recent exploration, unpublished material and accessible surface and subsurface exposures provide a valuable preliminary case study of the deposit. Examination of three transversal trenches and re-logging of eleven Rotary Air Blast (RAB) drill holes in the western part of the deposit reveal moderately to intensely sheared metasedimentary rocks of the lower Birimian formation such as mica schist, graphitic schist, quartzite, and a few pegmatite intrusions. Optical microscopic studies show that the deposit occasionally occurs in a complex mineral paragenesis of quartz ± calcite ± hornblende ± magnetite ± pyrrhotite ± rutile ± chalcocite ± graphite and other gangue minerals, often found around the boundaries of large magnesian ferrohornblende minerals, which tend to form quartz crystals. The Kambale deposit is characterized by numerous faults and shears, associated with brittle-ductile deformation at the NE part of the main shear with fewer faults and shears at the southern and western zones, generally trending E-W between 150ånd 320˚, dipping in NE-SW direction at an average of 060˚. The rocks have undergone medium-high grade metamorphism under high T/medium P facies typically estimated as (∼600-750 • C, 5.0–8.0 kbar), in amphibolite-granulite facies. The genesis of the flake graphite in Kambale is believed to be as a result of the high grade metamorphism, where deep-seated CO 2-rich fluid phase of crustal origin invaded the metamorphosed rocks. The intensity of the pore fluid pressures aided in the genesis of the graphite by hydraulic fracturing of the underlying rocks under regional syntectonic deformation.

Complex investigations of tetradymite Bi2Te2S from Župkov area (Slovak Republic) found as museum sample in Lviv
National University is carried out by methods of electronic microscopy, local microprobe analysis and X-ray diffraction. It
is established, that tetradymite occur as almost perfectly shaped crystals of rhombohedral and pinacoidal habits or as crystals with habit transitive between them. The main simple forms of crystals established are {0001}, {1011} and {0112}.
Tetra dymite crystals are commonly look like cutted trigonal pseudo-pyramids, lamellar crystals as well twinned formation
of tetrade-crystals. Chemical composition of the mineral has established based on data of statistical distribution of atoms
into crystallochemical positions and tetradymite formula is established to be similar to Bi1.86Sb0.14Te2S0.94Se0.06. Crystalline structure of the mineral is specified by using Rietveld method. The historical importance of the studied samples is also considered. Some data on tellurides of tetradymite group obtained earlier at their studying in the frame of joint international project "Comparative mineralogo-geochemical analysis Аu-Ag-Bi-Te-Se of mineralization in neovolcanites of Ukraine and Slovakia (region Carpathians)" carried out 2008—2010 years are also used.