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  • Open access
  • 182 Reads
Nb-Ta-Ti oxides in topaz granites of the Geyer granite stock (Erzgebirge Mts., Germany)

Nb-Ta-Ti-bearing oxide minerals (Nb-Ta-bearing rutile, columbite-group minerals, W-bearing ixiolite) represent the most common host in high-F, high-P Li-mica granites and related rocks from the Geyersberg granite stock in the Krušné hory/Erzgebirge Mts. batholith. The Geyersberg granite stocks forms a pipe like granite stock composed of fine- to middle-grained, porphyritic to equigranular topaz- Li mica granites, containing up to 6 vol. % of topaz. Intrusive breccias on the NW range of the granite stock are composed of mica schist- and muscovite-gneiss fragments enclosed in fine-grained aplitic granite. Granites are partly greisenised, mainly along of steeply dipping NW-SE, and NE-SW trending faults. Quartz-Li-mica-topaz greisens are mineralised by cassiterite, arsenopyrite, wolframite and molybdenite. The high-F, high-P Li-mica Geyersberg granites, which represent the youngest granite intrusions in the Western and Middle Krušné Hory/Erzgebirge plutons, are highly fractionated S-type granites (ASI = 1.2–1.5) with Nb/Ta ratio = 0.74–1.12 and depletion in high-field-strength elements (HFS). Columbite group minerals occur usually as anhedral grains that display patchy zoning. These minerals are represented by columbite-(Fe) with Mn/(Mn+Fe) ratio ranging from 0.07 to 0.32. The rare Fe-rich W-bearing ixiolite occurs as small needle-like crystals. The ixiolite is Fe-rich with relatively low Mn/(Mn + Fe) and Ta/(Ta + Nb) values (0.10–0.15 and 0.06–0.20 respectively). Owing to the high W content (19.8–34.9 wt. % WO3, 0.11–0.20 apfu), the sum of Nb + Ta in the ixiolite does not exceed 0.43 apfu. The Ti content is 1.7–5.7 wt. % TiO2 and Sn content is relatively low (0.3–4.1 wt. % SnO2)

  • Open access
  • 245 Reads
Two-stage SART process: A feasible alternative for gold cyanidation plants with high zinc and copper contents

The SART process (SP) has been successfully implemented in gold cyanidation plants to address issues associated with high cyanide-soluble copper content the ores. However, this process could produce a relatively low grade precipitate, descreasing the sale price, when gold plants have high zinc and copper content in their solutions. A potential option in this case would be use of a two-stage SART process (TSSP) to produce separate zinc and copper precipitates. The additional equipment involved with this process would increase the capital cost, thereby generating concerns about the optimal range of metal contents that could justify this option. This study presents a methodology to quantify the feasible range of Cu/Zn concentrations that would justify a two-stages SART process. The study is based on a thermodynamic model and a simple economic evaluation. Results show the TSSP is preferred when the Cu/Zn ratio ranges between 0.2 and 1.5 with copper concentration higher than 500 mg/L. The TSSP appears to be a viable option to consider for gold plants having concentrations of copper and zinc higher than 500 and 350 mg/L respectively.

  • Open access
  • 226 Reads
First zunyite-bearing lithocap in Greece: The case of Konos Hill Mo-Re-Cu-Au porphyry system.

Zunyite is a rare F- and Cl- bearing mineral related to advanced argillic alteration zones of porphyry/epithermal style mineralization and is considered as a pathfinder mineral towards high-grade Au ores. We report here the first occurrence of zunyite along with alunite, quartz, APS minerals, diaspore, pyrophyllite and kaolinite in the metallogenic province of Western Thrace.

The Konos Hill prospect in Western Thrace comprises a telescoped porphyry Mo-Re-Cu-Au system, overprinted by high-sulfidation mineralization. In low topographic levels, porphyry-style mineralization is exposed and comprises pyrite-chalcopyrite-bornite-molybdenite-rheniite-bearing quartz-stockwork. Host rocks are subvolcanic bodies of granodioritic composition that have suffered pervasive sericitic alteration. High-sulfidation epithermal-style alteration occupies the higher topographic levels and has caused significant overprinting of the porphyry-style mineralization and alteration. It consists of silicified zones related to N-S and E-W trending faults, which grade outwards to advanced argillic alteration assemblages. These assemblages are characterized by abundant alunite and quartz, with minor presence of diaspore, APS minerals, kaolinite, pyrophyllite and zunyite.

Zunyite forms euhedral crystals that reach in size up to 300μm. They sometimes include minor quartz and are associated with alunite, APS minerals and pyrophyllite. EPMA data revealed variations in the F and Cl content of zunyite, that range between 3.62-6.54 wt.% and 2.65-3.15 wt.% respectively. Alunite supergroup minerals display a wide compositional range and are represented by members of the alunite, beudanite and plumbogummite subgroups. Alunite and natroalunite constitute the most common advanced-argillic alteration minerals and are found in both quartz+zunyite and quartz+diaspore+pyrophyllite assemblages. Available mineral-chemical data favor the existence of compositions that cover a complete solid-solution series between Na- and K-rich varieties. Common mode occurrences comprise euhedral, tabular-shaped and rarely pseudocubic crystals. APS minerals are usually found as pseudocubic crystals forming the cores of tabular alunites. Analyzed compositions comprise woodhouseite (Sr-, Ce- and Sr-Ce- rich members were found). Diaspore forms aggregates of euhedral, coarse-grain crystals scattered in strongly silicified rock. Finally, pyrophyllite when present, forms acicular aggregates in the matrix along with diaspore and quartz.

Available data suggest that the formation of the studied advanced argillic alteration assemblages is hypogene and due to ascending magmatic fluids released by the subvolcanic bodies. Mineralogical variances in the different assemblages may reflect distinct degrees of hydrothermal alteration. Co-existence of zunyite, APS minerals and pyrophyllite could be used to set constraints on the physicochemical conditions of formation of the assemblage, as the volatile-rich nature of the minerals reflects a narrow range of pH and temperature in hydrothermal systems.

  • Open access
  • 254 Reads
The Ni-Bi-Au association at Kamariza and ‘km-3’, Lavrion ore district, Greece

The Lavrion ore district, located about 50 km southeast of Athens (Greece), contains a variety of ore types including porphyry Mo-W, skarn Fe-Cu-Bi-Te, carbonate-replacement Pb-Zn-Cu-Ag±Au-Bi and vein-type Pb-As-Sb-Ag and Pb-Ni-Bi-Au (Solomos et al. 2004; Voudouris et al. 2008; Bonsall et al. 2011; Kolitsch et al. 2015). Mineralization was synchronous to the intrusion of a Miocene granodiorite body in the footwall of the Western Cycladic Detachment System and related felsic dikes and sills within marbles and schists, which locally cross-cut the detachment. Carbonate-sericite altered microgranodioritic dikes and sills at Kamariza are crosscut by porphyry-style quartz-sericite-calcite stockworks hosting pyrrhotite, pyrite, arsenopyrite, chalcopyrite and sphalerite (e.g. the same metallic minerals present in the carbonate-replacement and vein ores). The dikes and sill display enrichment in Ni (up to 220 ppm), Cu (up to 175 ppm), As (up to 510 ppm), Mo (up to 6 ppm) and Pb (up to 830 ppm), as measured by ICP-MS. The Ni-Bi-Au association at the Clemence mine in Kamariza is a vein-type mineralization developed at the contact between marbles and schists. The mineralization also expands in the marbles unit, forming carbonate-replacement bodies. It consists of native gold and bismuthinite intergrown with gersdorffite, enclosed in galena. Bulk ore analyses reveal Au and Ag grades exceeding 100 ppm, Pb and Zn > 1 wt. %, Ni up to 9700 ppm, Co up to 118 ppm, Sn > 100 ppm and Bi > 2000 ppm. New mineralogical and mineral-chemical data from the Ni-Bi-Au association suggest gold deposition with oscillatory zoned gersdorffite following initial deposition of pyrite and arsenopyrite. Oscillatory zoning in gersdorffite is related to variable As, Ni and Fe contents, indicating fluctuation of arsenic fugacity in the hydrothermal fluid. Chalcopyrite, tennantite and enargite rimming gersdorffite suggest an evolution towards higher sulfur fugacity in the mineralization with time. Stannite enclosed in pyrite and native antimony enclosed in galena are decribed here for the first time in the Clemence ore assemblage. At the ‘km-3’ locality, the Ni sulfides and sulfarsenides, vaesite, millerite, ullmannite and polydymite, are enclosed in gersdorffite and/or galena. At this location mineralization occurs in the form of calcite and galena veins crosscutting and cementing brecciated marbles, within the detachment fault. Mineralization is enriched in Mo (up to 36 ppm), As and Ni (both >1 wt. %), Co (up to 1290 ppm), whereas other elements occur in lesser amounts: Te (up to 2 ppm), Sn (up to 8.5 ppm), Bi (up to 1.3 ppm). Gersdorffite at ‘km-3’ is homogenous and contain less Fe (up to 2 wt. %) than that from the Clemence mine (up to 9 wt. %), probably related to lower temperatures of their formation. The geochemical and mineralogical data from this study support previous models for a magmatic contribution of metals to the ore system, although a remobilization from previous mineralization and/or country rocks cannot be ruled out.

  • Open access
  • 402 Reads
Gold deposits in Greece: Hypogene ore mineralogy as a guide for exploration

A common feature of precious metal mineralization in Greece is the close relationship between gold and silver with other trace minerals incorporating bismuth, tellurium and selenium in their structure. These minerals can be considered as pathfinders for gold as they may guide exploration to discover distinct types of gold-bearing ores. Primary gold mineralization in Greece can be subdivided in three groups regarding the mineral associations with gold: (A1) mineralization where native gold and Au-Ag tellurides accompany either Bi-sulfosalts, native Bi and reduced-type Bi-sulfotellurides (joséite-A, joséite-B, pilsenite) at Koronouda, Laodikino/Kilkis area, Stanos, Olympias-Stratoni and Fissoka at Chalkidiki area and Angistron Mt/W. Rhodope), or (A2) accompany Bi-sulfosalts with oxidized-type Bi-sulfotellurides (e.g. tetradymite and tellurobismuthite) typical for Aberdeen, Palea Kavala, Thasos island, as well as for the calc-alkaline and alkaline-hosted porphyry and epithermal deposits/prospects in western Thrace, Limnos island and Skouries; (B) deposits which lack tellurides but include Bi-sulfosalts and native gold (e.g. the carbonate replacement deposit of Lavrion, the porphyry-Cu-Mo-Au deposits of Maronia and Stypsi, Lesvos Island, and the intrusion-related Kimmeria Cu-Mo-Au deposit); and (C) deposits/prospects where native gold and Au-Ag-tellurides and other base metal tellurides are abundant and Bi-tellurides and Bi-sulfosalts are missing (the metamorphic rock-hosted quartz veins at Panormos/Tinos and Kallianou/Evia Islands, and the epithermal shallow submarine mineralization at Milos). Bismuth and tellurium are considered to be derived from magma and recognition of bismuth sulfosalts and bismuth tellurides, as well as of various types of base (and precious) metal tellurides in the mineralization, is a strong evidence of magmatic-hydrothermal contribution and of adjacent concealed intrusives (e.g. Perama Hill and Pefka deposits are cases where no granitoids are exposed). The absence of bismuth minerals and the presence of precious and base metal tellurides (as is the case for Milos, Tinos and Evia islands) may still suggest magmatic contributions but in more distal setting from a buried granitoids at depth. Selenium (and/or bismuth) bearing galena and Se-bearing bismuth chalcogenides present at Kimmeria intrusion-hosted veins, at Lavrion, as well as in several porphyry-epithermal deposits in northern Greece (e.g. Kassiteres-Sapes, Pagoni Rachi, Perama Hill, Pefka and Skouries) are indicative of high-temperature, initial stages of ore deposition from magmatic-hydrothermal fluids, and proximity to porphyry mineralized centers. When recognized in a mineralization as an accessory mineral, Se-bearing galena could guide exploration towards unexposed granitoids. Bornite and molybdenite are present in the potassic and sericitic alteration zones of Skouries and Pagoni Rachi porphyry deposits, where they are intimately associated with native gold and gold-silver tellurides. However bornite may also occur in intermediate-sulfidation epithermal veins at Kassiteres-Sapes and Pagoni Rachi areas and molybdenite at Stanos and Syros Island without any obvious relationship to a granitoid. Both minerals can be applied for discovery of high temperature mineralized zones in the system.

  • Open access
  • 191 Reads
A review on the critical and rare metals distribution throughout the Vertiskos Unit, N.Greece

The undisturbed supply of critical and rare metals is critical for the robustness and sustainability of the advanced technological industry of the European Union (EU). Large demands and a low domestic production characterize the availability of these mineral resources within the EU. Since 2008, several EU funded research projects have highlighted the domestic exploration and exploitation possibilities of some specific European regions. Throughout the SE Europe the Serbo-Macedonian metallogenic province (SMMP) in northern Greece is highlighted as one of the most promising exploration targets. The metamorphic terrain of the Vertiskos Unit forms the geological basement of the SMMP in northern Greece, and hosts several Oligocene-Miocene ore deposits and mineralization occurrences. Ancient and modern mining activities mostly targeted the southern part of the Greek SMMP (Chalkidiki Peninsula), while the northern part was subjected to a diachronic occasional pre-industrial exploitation. Thus, by taking into consideration the modern exploration and exploitation techniques, the northern part could be characterized as a greenfield area. The base (Cu, Pb, Zn, Fe, Mn) and precious (Au, Ag) metals endowment of the Vertiskos Unit is well-documented and among the most important mineralization of the region are the Pontokerasia Cu-Mo-Au-porphyry deposit, the Vathi Cu-Au-U±Mo porphyry deposit, and the Skouries Cu-Au porphyry deposit. However the critical and rare metals endowment of the region lacks any thorough examination. Several porphyry mineralizations hosted in high-K calc-alkaline magmatic rocks (e.g. Vathi, Gerakario, Skouries), and vein type mineralization hosted in shear-zones (e.g. Rizana, Stanos, Kolhiko, Laodikino, Stefania, Koronouda, Drakontio, Nea Madytos) are reported being enriched in Sb, Bi, Te, Co, Sn, W, Ga, Ge, In, Ta, REEs and PGEs. In this publication we review the critical and rare metals endowment of these ore mineralizations in an effort to summarize and highlight the exploration potential of the region.

  • Open access
  • 130 Reads
Boiling assemblages in the Kupel occurrence, Krumovgrad goldfield, SE Bulgaria

This paper presents a study on boiling assemblages in the Kupel occurrence, as boiling was evidenced by the presence of vein adularia and platy calcite. Fluid inclusion evidence is not available since the present fluid inclusions are very small in size for investigation under optical microscope. Boiling assemblages occur in two types of auriferous mineralization hosted by supradetachment, grey fine-grained arkosic sandstones and presented by (i) veinlets of quartz-adularia and (ii) veinlets of platy calcite. In quartz-adularia veinlets micron-sized electrum aggregates form globular shapes, which reach 800 µm across and are arranged along the veinlet length. In cross-sections electrum aggregates display abundant silicate-filled pores of a few microns in size. Globular geometry of the electrum aggregates and their arrangement along the veinlet length suggest collectively that these globules were flowing particles - flocs but not colloidal particles since the latter are much smaller. In these veinlets electrum is intergrown with micron-sized chalcopyrite, galena, hessite and greenockite. The auriferous calcite veinlets are formed later than the auriferous quartz-adularia ones, since the first clearly has intersected or brecciated the latter. Electrum in the calcite veinlets forms accumulations only in portions of sharp thickness expansions after throttle portions, which are barren. This suggests that electrum has been transported by a flowing fluid, in a particulate form and deposited due to pressure drop during hydrofracturing, as the electrum particles have been arrested in low velocity (expanded) portions of ore conduits. The auriferous assemblages in the Kupel occurrence indicate high effectiveness of boiling for deposition of Au, Ag, Cu, Pb, Cd and Te through collective loss of H2, CO2, H2S and H2Te what is in complete accord with recent studies on modern terrestrial geothermal fields. Methods used comprise observations under binocular, optical and scanning electron microscope, and electron microprobe analysis.

  • Open access
  • 356 Reads
REE distribution in the black sands in the area of Loutra Eleftheron, Kavala, northern Greece: mineralogical and geochemical characterization of fractions from grain size and magnetic separation analysis

Black sands from the area of Loutra Eleftheron in Kavala, northern Greece, are known for their enrichment in rare earth element (REE) bearing minerals. REE are critical metals used in advanced applications and are of high demand in the European Union (EU). This work employs scanning electron microscopy (SEM), X-ray diffraction and XRF analysis to characterize the products from laboratory grain size separation and magnetic separation (high intensity magnetic separators - HIMS). The information gathered can be used to identify the optimum fraction for REE recovery which is essential for the design of a beneficiation process.

Mineralogical and geochemical analysis were performed on a composite sample. The studied sample consists of the following heavy minerals: mainly magnetite, ilmenite, rutile, zircon and allanite. Allanite is the major host mineral for light REE (LREE) and monazite is subordinate. Most of the allanites exhibit zoning, with the marginal areas of the grain showing relative depletion in REE. Specifically, the chemical composition of the peripheral zones indicates replacement of the allanite with zoisite and epidote.

Characterisation of the magnetic separation and grain size fractions allowed the following conclusions to be made: a) The magnetic fraction of the black sand is strongly enriched in the LREE, relative to the non-magnetic fraction, and is found 1.62 times higher than the bulk composition. Allanite is the major host mineral for LREE in the magnetic fraction. b) A combination of SEM/EDS and XRF analysis of the different grain size fractions showed LREE enrichment in the fractions – 0,425 +0,150 mm, and a maximum enrichment in the - 0,355, + 0,212 mm.

  • Open access
  • 95 Reads
Cr release from Cr-substituted goethite during the aqueous Fe(II)-induced recrystallization

The interaction between aqueous Fe(II) (Fe(II)aq) and iron (hydr)oxides is an important reaction of iron cycle and plays a critical role in the environmental behavior of heavy metal in soils. The metal substitution has been reported to decrease the Fe atom exchange rates between the Fe(II)aq and metal-substituted iron (hydr)oxides as well as inhibiting the recrystallization of iron (hydr)oxides, whereas the environmental behaviors of the substituted metal during the processes remain unclear. In this study, Fe(II)aq-induced recrystallization of Cr-substituted goethite (Cr-goethite) and the sequentially release of substituted Cr were investigated under different conditions. The results of stable Fe isotopic tracer and Mössbauer characterization studies show that Fe atom exchange occurred between Fe(II)aq and structural Fe(III) in Cr-goethites, during which Cr-goethites were recrystallized. The Cr substitution inhibited the rates of Fe atom exchange and Cr-goethite recrystallization. During the processes, Cr were released from Cr-goethite and Cr-goethites with higher Cr-substituted contents released more. Highest Fe atom exchange rate and most amount of Cr release were observed at pH 7.5, while no change in mineral phase after reaction for 30 days. At a lower pH of 5.5 or a higher pH of 8.5, significantly less exchange and Cr release occurred. The releases of Cr were positively correlated with the Fe atom exchanges rates, suggesting the driving force of sorbed Fe(II) for the Fe atom exchange and Cr release. The release and re-incorporation of Cr simultaneously occurred during the Fe(II)aq-induced recrystallization of Cr-goethites, especially at the late stage of the reactions. Our findings indicate that dynamic changes of Cr forms relating to Fe(II)aq-induced recrystallization of iron (hydr)oxides should be considered when evaluating the soil Cr pollution in Fe-rich soils.

  • Open access
  • 170 Reads
Formation of Mn-skarn Ores at Thapsana Mines, Paros Island, Attico-Cycladic Metallogenetic Massif, Greece

Mn-skarn ore deposits are relatively infrequent worldwide. A typical example of a Mn-skarn in the Attico-Cycladic Metallogenetic Massif is located at the mining area of Thapsana, Paros Island. The skarn occurs adjusted to the Thapsana biotite-garnet-tourmaline-lepidolite, highly sericitized, leucogranite apophyses of the Paros granitoid and related pegmatites and aplites dated from 11.5 to 7.5 Ma. The Mn-skarns orebodies occur as lenses and NE-trending veins hosted in the Cyclades Blueschist Unit (CBU) marbles and intercalated calcic schists. They comprise two discontinuous paragenetic zones (with widths of ≤ 10 m): A zone contain vesuvianite, Mn-enriched salite to johannsenite-diopside and spessartine with cores enriched in grossular component (Sps~75Grs~15) placed close to the Thapsana leucogranite and a zone of grossular (Sps~85Grs~5), actinolite to Mn-cummingtonite (with Mn ~ 0.6 apfu) and phlogopite more distal from the leucogranite. The Mn-skarns are crosscut by later WNW- to W-trending veins filled with Ca-K-Mg-bearing pyrolusite, manganite, rhodonite and rhodochrosite, carbonates, hydroxylapatite and johnbaumite.

The Mn-ores occur as massive aggregates or disseminated comprising jacobsite, hausmannite, Mn- enriched magnetite, braunite and hollandite (with crystals of ≤ 4cm). Occasionally jacobsite and hausmanite display oriented intergrowths. The ore paragenesis also includes secondary pyrolusite, manganite, rhodonite, rhodochrosite, cryptomelane, manjiroite, vernadite and supergene Fe-oxides. Geothermo-oxygen-barometry suggests that the main zones of the Mn-skarns at Thapsana have been formed at temperatures ranging from ~ 440º to ~ 510ºC, pressures of 0.11 to 0.12 GPa and logfO2 values just below the magnetite-hematite buffer. Almost constant average isotopic compositions obtained from the Mn-ores (n = 10) of δ44CaBSE and δ26MgDSM-3 of 0.5 ± 0.05 and -0.6 ± 0.1 and δ18O and δD of 7.2 ± 0.5 and -92 ± 2 per mil, suggest a magmatic source for the metasomatic ore fluids related to the Thapsana leucogranite which have also interacted and isotopically equilibrated with the host CBU marbles.

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