Permian–polysulphide-siderite–barite–haematite deposit Rude in Samoborska Gora Mts., Zagorje–Transdanubian zone of the Inner Dinarides

Samoborska Gora Mts. is situated within westernmost part of the Zagorje–Mid–Transdanubian zone of the Inner Dinarides. The Samoborska Gora Mts. consists dominantly of Permian unmetamorphosed siliciclastic sediments and evaporites, overlain by Lower Triassic sediments. Rude mineralization is hosted by Permian siliciclastic sediments, beneath gypsum and anhydrite strata. Central part of the deposit consists of 1.5 km long stratabound mineralization, grading laterally into ferruginous sandstone and protruding vertically into a gypsum–anhydrite layer. Siderite–polysulfide–barite–quartz veins are located underneath the stratabound mineralization. Late stage galena–barite veins overprints the formerly formed mineralization types. The Rude ore deposit was generated by NaCl±CaCl2–H2O solutions. Stratabound mineralization was precipitated from solutions with salinities between 7 and 11 wt. % NaCl equ., homogenizing between 150°C to 230°C. Vein type mineralization derived from solutions with salinities between 4 and 20 wt. % NaCl equ., homogenizing between 80°C and 160°C, while late stage galena–barite veins were precipitated from solutions with salinities between 11 and 16 wt. % NaCl equ., homogenizing between 100°C to 140°C. Fluid inclusions bulk leachate chemistry recorded Na+>Mg2+>K+>Ca2+>Li+ and Cl–>SO42– ions. Sulfur isotope composition of barites and overlying gypsum steams from the Permian seawater sulfate, supported by increased Br– content, which follows successively the seawater evaporation line. The sulfur isotopic composition of sulfides varies between –0.2 and +12.5 ‰, as a result of thermal reduction of Permian marine sulfate. Ore–forming fluids were produced by hydrothermal convective cells (reflux brine model) and derived primarily from Permian seawater,- modified by evaporation and interaction with the Permian sedimentary rocks. Rude deposits in Samoborska Gora Mts. may be declared as a prototype of the Permian siderite–polysulfide–barite deposits, products of the rifting along the passive Gondwana margin, in the Inner Dinarides, and their equivalents in extension northeastward into Zagorje–Transdanubian Zone and Gemerides, and southeastward to Hellenide–Albanides.Samoborska Gora Mts. is situated within the westernmost part of the Zagorje–Mid–Transdanubian zone of the Inner Dinarides. The Samoborska Gora Mts. predominantly consists of Permian unmetamorphosed siliciclastic sediments and evaporites, overlain by Lower Triassic sediments. Rude mineralization is hosted by Permian siliciclastic sediments, below gypsum and anhydrite strata. The central part of the deposit consists of a 1.5 km long stratabound mineralization, grading laterally into ferruginous sandstone and protruding vertically into a gypsum–anhydrite layer. Siderite–polysulphide–barite–quartz veins are located below the stratabound mineralization. The stratiform part of the deposit is situated above the stratabound and consists of haematite lajer with barite concretions and veinlets. Late stage galena–barite veins overprint earlier types of mineralization. The Rude ore deposit was generated by predominantly NaCl ±} CaCl2–H2O solutions. Detrital quartz from stratiform mineralization was precipitated from solutions with salinities between 7 and 11 wt. % NaCl equ., homogenizing between 150 °C to 230 °C. Stratabound/siderite–polysulphide–barite–quartz vein type mineralization was derived from solutions with salinities between 5 and 19 wt. % NaCl equ., homogenizing between 80 °C and 160 °C, while late stage galena–barite veins were precipitated from solutions with salinities between 11 and 16 wt. % NaCl equ., homogenizing between 100 °C to 140 °C. Fluid inclusion bulk leachate chemistry recorded Na+>Mg2+>K+>Ca2+>Li+ and Cl–>SO4 2–ions. Sulphur isotope composition of barites and overlying gypsum stems from Permian seawater sulphate, supported by increased Br– content, which follows successively the seawater evaporation line. The sulphur isotopic composition of sulphides varies between –0.2 and +12.5 ‰, as a result of thermal reduction of Permian marine sulphate. Ore–forming fluids were produced by hydrothermal convective cells (reflux brine model), and were derived primarily from Permian seawater, modified by evaporation and interaction with Permian sedimentary rocks. Rude deposits in SamoborskaGora Mts. may be declared as a precursor? of the Permian siderite–polysulphide–barite deposits (products of rifting along the passive Gondwana margin), in the Inner Dinarides, and their equivalents extending northeastward into the Zagorje–Transdanubian Zone and the Gemerides, and southeastward to the Hellenide–Albanides

Ore forming fluids in the Allchar Au-Sb-As-Tl deposit, FYR Macedonia

The Allchar Au-Sb-As-Tl mineral deposit is a Carlin-type mineralization with a zonal distribu-tion of mineral parageneses and alterations. The zonation is a result of a spatial distribution of ore-forming fluids with different thermal and chemical characteristics as proven by a fluid inclusion study. Three zones are distinguished: 1. a southern Au-Sb-As zone, 2. a central zone, which hosts a Au-Sb-As-Tl-Hg mineralization, and 3. a northern As-Tl zone. Homogenization temperature and sa-linity decrease steadily from the southern to the northern zone of the deposit due to cooling and di-lution of the fluids

The ore forming fluids in the Allchar polymetallic ore field, FYR Macedonia.

The Allchar polymetallic ore field is located at the southern margin of the Vardar zone, 110 km SE from Skopje, FYR Macedonia. Mineralization of Allchar is subdivided into three zones: (1) High temperature sulfide mineral paragenesis represented mainly by Sb and As mineralization ; (2) Sulfide mineralization barren of Sb and enriched in As and Tl and (3) Low temperature mineral paragenesis represented by barite, native sulfur, calcite, chalcedony and opal (IVANOV, 1986). The Allchar deposit is related to a Pliocene volcano-intrusive complex which occurs along a major regional fault zone between the rigid Pellagonian block on the west and the labile Vardar zone on the east. The basement is composed of Triassic sediments, the Jurassic ophiolites and the Cretaceous sediments (JANKOVIĆ & JELENOVIĆ, 1994). The rocks of volcano-intrusive complex range from andesite-quartz latite to rhyolite and trachyte (BOEV, 1993). Mineralization is spatially related to zonal hydrothermal alterations. The main types of alterations are silicification and argilization. The silification in the southern part of the ore field (zone I) represented by small quartz grains is related to antimony and gold mineralization. Argillitization is mainly developed in the volcanic rocks. In the northern part of the ore field (zone III) silification is represented by occurrence of chalcedony and opal (BOEV, 1993). 2. Samples and methods A fluid inclusion (FI) study was carried out to estimate the P-T conditions during mineralization and to characterize the mineralizing fluid. Microthermometric measurements were performed on primary FIs within doubly polished, ~0.5 mm thick, wafers of: (1) Quartz associated with high temperature sulfide mineralization (zone I) ; (2) Realgar and orpiment associated with sulfide mineralization barren of Sb and enriched in As and Tl (zone II) and (3) Opal associated with low temperature mineralization (zone III). Ultraviolet (UV) fluorescence microscopy was used to estimate the presence of hydrocarbons bearing inclusions

Fluid inclusions and K/Ar dating of the Allsvar Au-Sb-As-Tl mineral deposit, Macedonia

The Allšar Au-Sb-As-Tl mineral deposit, Macedonia, occurs in the southern part of the Vardar zone. The deposit carries Carlin-type of mineralization hosted by calcareous sedimentary complex. Mineral assemblages and alterations display characteristic zonal distribution. According to the fluid inclusion data, mineral deposition occurred as a result of cooling, dilution and neutralization of the ore-bearing fluids. Neogene magmatism (4.6 to 5.8 Ma) served as the heat source responsible for driving convective hydrothermal circulation at the Allšar deposit

Comparison of the Allchar Au-As-Sb-Tl Deposit, Republic of Macedonia, with Carlin-Type Gold Deposits

The Allchar Au-As-Sb-Tl deposit is situated in the western part of the Vardar zone, the main suture zone along the contact between the Adriatic and the Eurasian tectonic plates. It is spatially and temporally associated with a Pliocene (~5 Ma) postcollisional high-K calc-alkaline to shoshonitic volcano-plutonic center. The Allchar deposit shares many distinctive features with Carlin-type gold deposits in Nevada, including its location near a terrain-bounding fault in an area of low-magnitude extension and intense magmatism. The mineralization is mostly hosted in calcareous sedimentary rocks at intersections of high-angle faults in permeable stratigraphy. The alteration types (carbonate dissolution, silicification, and argillization), ore mineralogy (auriferous arsenian pyrite and marcasite, stibnite, realgar, orpiment, and lorandite), high Au/Ag ratios, and low base metal contents are also typical of Carlin-type gold deposits in Nevada. However, the Allchar deposit differs from Nevada Carlin-type gold deposits as follows: it is an isolated Au prospect with a close spatial and temporal relationship to a shoshonitic volcano-plutonic center in a mineral belt dominated by intrusion-related Cu-Au porphyry, skarn, and hydrothermal polymetallic deposits. The deposit is clearly zoned (proximal Au-Sb to distal As-Tl), it has a significantly higher Tl content, trace elements in pyrite and marcasite are homogeneously distributed, and synore dolomitization is a widespread alteration type. Gold mineralization is most abundant in the southern part of the deposit. It occurs mostly as invisible Au in disseminated pyrite or marcasite and as rare native Au grains. Gold mineralization is accompanied by intense decarbonatization and silicification. Fluid inclusions and the hydrothermal alteration mineral assemblage indicate that Au was deposited from hot (>200°C), saline (up to ~21 wt % NaCl equiv), moderately acidic (pH <5) fluids that carried traces of magmatic H2S and CO2. In the calcareous host rocks, mixing of such fluids with cool, dilute, near-neutral groundwater triggered deposition of Au and Fe sulfides. In Tertiary tuff, isocon analysis shows that sulfidation of preexisting Fe minerals was a critical factor for deposition of Au and Fe sulfides. Antimony mineralization prevails in the central part of the deposit, and it is mostly associated with dark-gray to black jasperoid. Stibnite, the most common Sb mineral in the Allchar deposit, occurs as fine-grained disseminations in jasperoid and as fine- to coarsely crystalline masses that fill vugs and fracture zones lined with drusy quartz. Fluid inclusions entrapped by stibnite-bearing jasperoid, quartz, and calcite crystals suggest that stibnite was deposited from more dilute and cooled fluids (aqueous-carbonic fluid inclusions: 6.0–3.5 wt % NaCl equiv, TH = 102°–125°C; aqueous fluid inclusions: 14.5 and 17.1 wt % NaCl equiv, TH = 120°–165°C). In contrast to stibnite, As sulfides (orpiment and realgar) and Tl mineralization are associated with argillic alteration. Fluid inclusions hosted by realgar, orpiment, dolomite, and lorandite record deposition from more dilute (2.6–6.9 wt % NaCl equiv) and relatively cold fluids (TH = 120°–152°C) enriched in K. Isocon diagrams show a tight link between Tl and the low-temperature argillic alteration as well as a significant correlation between Tl and K. The spatial relationship of Tl mineralization with dolomite suggests that Tl deposition was also promoted by neutralization of acidic fluids. The dD and d18O data obtained from gangue minerals and fluid inclusions indicate that magmatic fluid mixed with exchanged meteoric water at deep levels and with unexchanged meteoric water at shallow levels in the system. The d13C and d18O values of carbonate minerals and extracted fluid inclusions suggest mixing of carbonate rock buffered fluids with magmatic and atmospheric CO2. The sulfur isotope values of early disseminated pyrite and marcasite show that H2S was initially derived from diagenetic pyrite in sedimentary rocks. In contrast, Sb and As mineralization indicate a strong input of magmatic H2S during the main mineralization stage. Late-stage botryoidal pyrite and marcasite are depleted in 34S, which indicates a diminishing magmatic influence and predominance of sulfur from sedimentary sources during the late-mineralization stage. Fractionation of isotopically light sulfide species from isotopically heavy sulfates due to oxidation under increased oxygen fugacity cannot be excluded