AREQUIPA 1
AREQUIPA 1 tenements are in south-western part of Peru. The tenement area forms part of Coastal Batholith, which is known for number of metalliferous mines. Also, the area is known for extensive gold mining activity during colonial times. Some of the prominent mines in the tenement include Grande Veta, Charposa, Escondida etc., gold mineralization in the area is associated with narrow quartz veins (0.2 to 1.5 m wide), which were emplaced along NW-SE trending mylonitic shear zones within the tonalite-diorite-monzonite suite of rocks. Length of these veins vary from 10 meters to > 2000m.
Grande Veta is the longest vein, which extended for 2700m along the strike. Quartz-sericite and epidote alteration is common in the wall rocks. Mineralized quartz veins are whitish, massive to fractured, low sulphidic in nature and contain few visible grains of gold. Structural controls and other physical characters of the veins point towards “mesothermal” type gold mineralization.
The tenement area has experienced extensive informal mining during colonial times. These veins, which invariable occur on the slopes of the hills were accessed through adits and mined along the vein by making galleries. These galleries are generally 1x1m or 2x2m in dimension. Grande Veta has been mined for a length of 800m in more than 3 levels. Similarly, Charposa, Esconidia and Pothacas veins also experienced extensive mining activity.
It is understood that ancient miners concentrated only on high grade portions of the vein and were mining at an average grade of 16 g/t. As a result relatively lower grade ore of about 5g/t has been left in the waste dumps near the mine site. Such dumps were found around Grande Veta, Charposa and Escondida. Further, there is still ore left in the lower levels of these mines, which can be extracted after cleaning and stabilizing the upper levels.
Field studies and geochemical sampling carried out has indicated the following.
i) The quartz veins in the area contain high grades of Au, at times >10 g/t,
ii) Some of the wall rocks do contain significant amount of gold (~2-5 g/t), which were left unmined,
iii) quartz veins are structurally controlled and certain structural corridors can be identified for further exploration,
iv) The ancient mines hold potential to deliver additional resources through systematic exploration/drilling,
v) Extensional areas of the known mines, eg., Escondida, hold potential to contains new veins,
vi) Waste dumps around the mine sites contain high grade quartz, which can sustain a small pilot processing plant,
vii) Gold in the quartz veins is “free gold” type, bulk of which can be extracted through simple gravity circuit,
A big heap of mine reject or waste dump is found at the entrance of Grande Veta mine. This heap includes both vein quartz and wall rocks. It is believed that the Grande Veta was mined at an average grade of ~16 g/t and lower grade material was dumped outside the mine entrance. Previous reports indicate that the average grade of the dump is about 5 g/t.
5 samples were collected from the Grande Veta mine area. They include wall rocks within the mine, unmined portions of the vein quartz and waste dumps. Unmined quartz vein yielded a value of 2.99 g/t, where as wall rocks yielded values of 0.19 g/t and 0.72 g/t. Samples collected from the waste dumps yielded values of 5.78 g/t and 4.36 g/t, which confirms the previous understanding that the waste dumps contain high grade ore. Some of the samples from the dumps were pulverized, washed and panned, which has yielded many gold grains in the pan. It clearly shows that gold occur as free grains in the host rock, which can be extracted through simple beneficiation process.
