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GEOLOGICAL SETTING The Buchim porphyry Cu deposit (41.7° N, 22.3° E) is located in the contact zone between the Serbo-Macedonian Massif and the Vardar Zone approximately 90 km south-east from Skopje, Republic of North Macedonia. The total ore reserves have been estimated at 120 million metric tons with 0.3 % Cu and 0.3-0.5 g/t Au (SERAFIMOVSKI et al., 2016). The mineralization is spatially and temporary related to subvolcanic intrusions of the latitic and latitic-andesitic composition that intruded Precambrian gneisses, mica-schists and amphibolites of the Serbo-Macedonian Massif. The U–Pb zircon dating yielded the intrusion age between 24.19 ± 0.62 Ma and 24.51 ± 0.89 Ma (Lehmann et al., 2013). The Buchim Cu deposit hosts 4 ore bodies: 1. Vrshnik ; 2. Bunardzik ; 3. Central ore body and 4. Chukar. The Cu mineralization at the Vrshnik ore body is predominantly hosted by the andesitic intrusion along its contact with the Precambrian gneisses. The mineralization occurs in forms of disseminations and stockworks. The main ore mineral is chalcopyrite accompanied with variable amounts of pyrite, magnetite, hematite and quartz. FLUID INCLUSION STUDY The ongoing fluid inclusion study revealed that syn-ore quartz may host several generations of fluid inclusions indicating a complex evolution of hydrothermal fluids in the Buchim Cu-Au porphyry deposit. According to their petrographic characteristics at room temperature, the following types of fluid inclusions have been recognized: Type 1) Two- phase, L-rich inclusions (L+V) with the degree of fill around 0.8, ; Type 2) Two-phase, V-rich inclusions (V+L) with the degree of fill around 0.2 ; Type 3) Three-phase inclusions that consist of liquid, vapor and a transparent isotropic solid phase (L+V+S) ; Type 4) Four- phase inclusions that consist of liquid, vapor and two transparent isotropic solid phases (L+V+S1+S2) ; Type 5) Four-phase inclusions that contain liquid, vapor, a transparent isotropic solid phase and an opaque solid phase (L+V+S+O) ; Type 6) Polyphase inclusions with liquid, vapor, two transparent isotropic solids and an opaque solid phase (L+V+S1+S2+O) ; and Type 7) Polyphase inclusions with liquid, vapor, two transparent isotropic solids, a transparent anisotropic solid phase and an opaque solid phase (L+V+S1+S2+ S3+O), where L stands for liquid, V for vapor, S for transparent solid and O for opaque phase (FIGURE 1 & 2). The inclusions with opaque minerals (Types 5-7) have been interpreted as entrapped ore-forming fluids. They are characterized by high homogenization temperatures (380-680ºC) and high salinities (26.9-74 wt.% NaCl equiv.). A broad range of homogenization temperatures and salinities indicates that mixing with colder and diluted fluids affected deposition of the Cu-Au mineralization. The main ore-forming phase was followed with several barren hydrothermal overprints (Types 1-4). Comparing to the ore- bearing inclusions, the homogenization temperatures of the barren L+V+S inclusions are somewhat lower (260-600 ºC) as well as their salinities (30.8-54.5 wt.% NaCl equiv.). The L+V inclusions are characterized by the lowest recorded temperatures of homogenization (218- 420 ºC) and salinities (6.5-29 wt.% NaCl equiv) (Jurković et. al., 2019). |
