| Keywords [eng] |
A-type, Kabeliai intrusion, granite, Cu-Mo mineralisation, oxygen fugacity, oxidised magma, emplacement conditions, albitization, pressure, microstructural description, mineral chemistry, water content, volatiles. A-tipas, Kabelių intruzija, granitas, Cu-Mo mineralizacija, deguonies aktyvumas, oksiduota magma, albitizacija, slėgis, mikrostruktūrinis aprašymas, mineralų chemija, vandens kiekis, lakiosios medžiagos. |
| Abstract [eng] |
The Mesoproterozoic A-type Kabeliai intrusion, located in southern Lithuania, has attracted attention due to minor differences from the AMCG suite and the A-type Mazury Complex in northern Poland. Of particular interest is the M7 borehole, where disseminated vein-style mineralisation has been identified, containing up to 3% Cu and 1% Mo. The M7 borehole granites are K-feldspar-bearing granitoids intermixed with mafic xenoliths and enclaves, and they exhibit varying degrees of metasomatic alteration, particularly albitization. This study aimed to investigate the M7 borehole to reconstruct the conditions of intrusion emplacement and subsequent alteration that might be related to Cu-Mo mineralisation. Four thin sections were investigated and analysed using Scanning Electron Microscopy (SEM) with Energy Dispersive Spectrometer (EDS) and Electron Probe Micro-Analyser (EPMA) with Wave-Length Dispersive Spectrometer (WDS). Additionally, multiple geothermometric and geobarometric methods were conducted. Igneous magma started to crystallise at ~870–847 °C (zircon) and ~850 °C (apatite). The homogenous amphibole average crystallisation temperature was 759 °C, while final solidification was recorded in biotites at an average of 579 °C. The pressure estimates for both amphiboles (avr. 176 MPa) and biotites (avr. 130 MPa) show the upper crust emplacement. The post-magmatic activity and late-stage melt crystallization are marked by the re-equilibration obtained temperatures of apatite, apatite-biotite (773.3 °C and 652 °C) and formation of secondary biotite at 525 °C. The oxygen fugacity (f(O2)) indicates an oxidised magmatic origin, with values around NNO+1. During post-magmatic decompression (average pressure ~97 MPa), f(O2) increased to conditions near the hematite–magnetite (HM) buffer, facilitating Cu-Mo mineralisation. This is further supported by the volatile component ratios in secondary biotites, which suggest alteration by a Cl-rich (saline) hydrothermal fluid. |
