Summary:
The Baita Plai mineralisation in geological terms is the most important manifestation of skarnhosted mineralisation in the Apuseni Mountains. The mineralisation hosts a large number of mineral species (about 90), some of which were described for the first time in the world (rezbanyite, szaibelyite or ascharite, and kotoite).
The main economic minerals, notably Cu, Pb, Zn, Au, Ag, Mo, Bi, W, and B, are concentrated in favourable sites due to the interaction of local faults (notably the Blidar contact) and a number of lesser fractures that have localised the mineralised veins, magmatic alteration, and favourable host rock lithologies (limestone and dolomites).
The orebody is hosted within Triassic limestones and dolomites, in faulted contact with underlying Permian shales across the Blidar fault. The skarn alteration is related to a granite intrusion which is interpreted to lie beneath the sediments as at yet an undetermined depth. Dykes of granitic, andesitic and lamprophyre origins cut the sediments at high angles but are reported to be pre-skarn. The host limestones and dolomites have undulating sub-horizontal dips, varying from 0-30 degrees.
A mineralogical study on metallurgical samples sent to Grinding Solutions (UK) was conducted during 2020 in which the main copper bearing minerals were identified as chalcopyrite, bornite and chalcocite, the main lead bearing mineral is galena and the main zinc bearing mineral is sphalerite. The dominant silver bearing minerals were identified as hessite and tetrahedrite.
The skarn mineralisation is hosted in several subvertical pipe-like bodies, often with tree-like branched geometries. Current mining is restricted to solely within the Antonio skarn. The Antonio North skarn is located approximately 300 meters to the north east of the Antonio skarn and is accessible from the same underground development structure serving the Antonio skarn on 18 level. It is postulated that the Antonio 1 and 2 pipes may merge at depth a few hundred metres below Level 18, forming a substantially larger orebody.
In plan view, the Antonio skarn is an elliptical shape with dimensions of approximately 160- 250 meters on strike and approximately 10-20 meters wide across strike. Within the skarn, the economic mineralisation forms lenses, veins and pods 1.5 – 20 meters wide, and of widely varying orientations.
The margins of the mineralisation are sharp against the calcareous country rock and visual identification of the contacts ensures minimal mining dilution.
The Antonio skarn is shown to be vertically zoned with gold and silver caps and with lead and zinc being of higher grade in the upper levels. Copper grades show an increase with depth and the recent drilling has provided evidence of a high correlation between copper, gold, silver and bismuth grades. A moderate correlation between lead and silver has been observed in the recent data. As copper gold and silver are major contributors to the mine economics, increasing grade at depth is an attractive target.