Mindoro Resources Ltd. (TSXV: MIO; Frankfurt: OLM) reports that high gold recoveries were obtained in a second round of column leach tests of coarse-crush mineralized material for a small bulk sample from the Archangel Project, Philippines. Mindoro is carrying out more detailed evaluations aimed at establishing the open-pit, heap-leach potential of the prospect.
Epithermal gold-silver replacement mineralization at Archangel is associated with silicification of an extensive, permeable volcanic tuff horizon. Related gold-in-soil anomalies extend semi-continuously over at least four kilometers by one kilometer; to date, geological mapping and reconnaissance rock sampling has traced the mineralization a distance of at least two kilometers.
Previous drilling in the 1990s by another company intersected low-grade gold mineralization, averaging about 0.7 grams per tonne (g/t), in an area of approximately 600 meters by 400 meters. Mineralization is open in several directions. Since the mineralization is near-surface and within the grade ranges being heap-leached elsewhere in the world, it is being evaluated for its open-pit, heap-leach potential. Preliminary bottle roll metallurgical test work, reported on January 14, 2004, was largely positive.
For a more detailed test, a 245 kilogram sample was collected from a trench and submitted to Metcon Laboratories in Australia. Results were reported in a release dated July 19, 2005. Head grade was 3.58 g/t gold and 51 g/t silver. The material was crushed to 12.7 millimeters (0.5 inch). The material leached exceptionally well, with 87.1 percent extraction of gold after only seven days. This high gold extraction is exceptional.
Because of the encouraging results at the minus 12.7 millimeter crush size, it was decided to carry out a second column test at a much coarser crush size of minus 50 millimeters. Feed weight for this test was 183 kilograms and agglomeration was carried out using 2 kg/t of cement. Calculated feed grade is 3.89 g/t gold. After 15 days, 70 percent of the gold had been recovered, and after 85 days, 81.7 percent of the gold recovered. Cyanide consumption was low.
The test work indicates that the sample tested is highly amenable to heap leaching even at a coarse crush size. The sample is likely of a higher grade than the bulk of the mineralization and leach characteristics will probably vary with grade and degree of oxidation.
It appears that cement, instead of lime, can be used as the agglomerating medium. The silver extraction at 10.2 percent was very low, despite the high silver head grade of 39 g/t, and more tests are required to reach a conclusion on the amenability of silver to leaching. Silver recoveries are characteristically low in gold-silver heap leach operations.
Additional samples, including non-oxide material at depth, will be collected for leach testing. The previous bottle roll testing of non-oxide material indicates at least some of the non-oxide material leaches well (see news release dated January 14, 2004).
Infill drilling is scheduled to begin in January 2006 to collect non-oxide samples for leach testing, to establish continuity of mineralization within the volcanic tuff horizon, and to establish the gold-silver resource potential.
The drill holes will be extended below the epithermal gold-silver mineralization to test for porphyry copper-gold mineralization. As reported in a press released dated May 11, 2005, a major geophysical survey detected strong and extensive chargeability and resistivity anomalies. Re-logging of old drill core indicates the presence of porphyry-related phyllic alteration associated with copper mineralization, immediately below the epithermal gold-silver mineralization. The epithermal mineralization has, therefore, been telescoped into the top of a porphyry system. This is a unique geological setting which allows exploration for both epithermal and porphyry mineralization at essentially the same erosion level.
Mindoro management is encouraged by the results from Archangel to date and considers these a strong basis for further evaluation of the project's economic potential. Evaluation of other porphyry copper-gold prospects elsewhere on Archangel is continuing, as is drilling on the Pica porphyry copper-gold system on the nearby Lobo Project. |
