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Queensland. December 2011
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Koloula
In the 1970's, Utah discovered three porphyry copper prospects situated along a major transform fault structure which also passes through Gold Ridge. The porphyry deposits are associated with a multi-phase diorite intrusive (the Koloula Igneous Complex) and are contained within the Tenements PL 02/05 (Koloula).
Utah carried out limited diamond drilling on the Mbina and Chikora porphyries in the early 1970s, obtaining results of up to 115m at 0.3 % copper at Chikora. Gold was not assayed at Chikora and only a few assays were done at Mbina.
Both Mbina and Chikora display classic porphyry zoning, with a central copper anomaly surrounded by lead-zinc haloes. Mbina also features a barren core with no copper. Mapping by a previous geologist at the time of Utah exploration indicates that Chikora lies within a major dilatant zone of which only part has been explored using soil geochemistry.
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Utah carried out almost no gold assaying. Later explorers obtained widespread gold anomalism during stream surveys but failed to locate significant hard rock mineralisation.
ARM undertook extensive rock chip sampling of drainages in the vicinity of the Mbina and Chikora prospects, obtaining results of up to 100m at 0.25g/t gold and 0.1 % copper at Chikora and 235m at 0.32g/t gold at Mbina. Up to 193g/t gold has been obtained from grab samples from narrow veins at Mbina. The gold zone at Mbina is also anomalous in zinc and lead and this zonation and the increase in gold tenor with elevation is consistent with a south-west Pacific model which predicts higher gold credits in the peripheral and higher zones around the intrusive porphyry core.
The known extent of the gold zone at Mbina is 2.0km x 0.5km north-south with 5m composite sample grades up to 5.5g/t gold in intrusive porphyry dykes and 71g/t in veins filling north-east oriented shear zones. This zone is supported by occurrences of gold and quartz veining in clay altered porphyry float in the headwaters of the Sutakiki River, a further 6km north-east.
The widespread gold anomalism at Mbina is broadly coincident with high potassium anomalies. A broad circular structure of potassium depletion is visible around the Mbina copper anomaly. This is consistent with a high potassium andesite lava host and parent intrusion (shoshonite affinity) and explains the occurrence of up to 5.5g/t gold in altered porphyry dykes at Mbina. In August 2007, Solomon Gold mobilized a third drilling rig to test the gold zone on the east side of the Koloula Porphyry system at Mbina. The drill hole, KL001 is testing a 2km x 300m wide zone trending nne – ssw, into which has been emplaced an epithermal (low temperature) quartz and carbonate vein grading 9.3g/t gold, 393 g/t silver, 0.9% copper and 0.75% zinc. The chemical signature indicates that the gold rich zone should be encountered at depth underneath this occurrence.
Investigation of the Chikora prospect revealed a 600m diameter gold-copper core with a surrounding gold-lead-zinc halo within a tonalite porphyry intrusive. ARM fieldwork has located a 200m x 800m open-ended gold-copper anomaly to the north-east which requires further investigation which the company intends to be subject to further mapping and sampling. The company has recently identified quartz and molybdenite filled veins which signify the potential for molybdenum credits in the mineralised porphyry system. Solomon Gold intends to drill test the Chikora porphyry system with angled drill holes in order to properly test vertical veining hosting the copper molybdenum and gold mineralisation.
The Koloula porphyries are interpreted as typical south-west Pacific porphyry deposits. The prospects are of interest because they appear to lie within a very similar structural setting to world class deposits in PNG, and display strikingly similar mineralogy and alteration patterns.
Assessment of the prospectivity of the area by Kenex has identified additional targets at Kolokoo and west of Mbina.
