Gold Anomaly Limited (ASX:GOA) Crater Mountain Major Multiple Mineralisation Events Associated with Porphyry System
Gold Anomaly Limited (ASX:GOA) report that the results from NEV027 (except base metal results from 500m – 840m) has now been received and analysed, with the highlight being the pervasive nature of gold mineralisation through the overlying Nevera volcanics and intrusions and down through the entire Chim Formation to its boundary with the deep porphyry at 1046m depth, after which the gold values drop off. The top 1,046m of the hole averages 0.25 g/t Au (no cut-off grade “COG” applied), which can be separated into a large number of significant zones of 0.25 to 1.0 g/t Au if a COG of 0.20g/t Au is applied.
– – Potential for multiple major mineralisation events now identified
– – Deepest level of gold mineralisation seen at Crater Mountain to date with the top 1,046m of the hole averaging 0.25 g/t Au (no COG applied)
– – Extends gold mineralisation identified at depth by approximately 500metres
– – Extends gold mineralisation by approximately 200metres to the south of the mixing zone
– – Porphyry intrusion intersected at 1,046m is considered to be an apophysis (arm) of the major deep intrusion responsible for baking the Chim Formation
– – Very strong base metal and silver mineralisation seen throughout the top 1,046m of the hole
– – Increased copper seen from the commencement of the porphyry intrusion highlights the potential for increased copper grades at greater depth
NEV027 results differ from earlier drill holes in the persistence of gold mineralization to a depth of more than 1,000m before terminating against a strongly veined but non-gold-bearing apophysis (peripheral arm potentially comprising a separate phase) of the major deep intrusion baking the Chim Formation. The great size of the intrusion is highlighted by the massive zone of altered sediments “the baked Chim Formation” (caused by heat from the intrusion which is a large central body considered likely to be surrounded by multiple peripheral porphyry apophyses such as intersected in NEV027 resulting from the final successive phases of porphyry development and mineralization as the central body cools) and starts at approximately 385mdown hole depth down to the intrusion at 1,046m.
The Company considers the persistence of gold mineralization to this previously unseen depth indicates that, whilst the gold in the mixing zone drilled in earlier holes is “suspended” at higher elevation under the prospect ridge and remote from its original deep source, the gold at depth in NEV027 is more directly related and closer to this source. It is thought that the source may be a different phase of porphyry apophysis of the main intrusion than that intersected by NEV027 or related to other activity in the regional deep crustal fractures hosting the intrusions.
NEV027 results are the deepest that gold has been intersected at Crater Mountain and highlight the sheer size of the mineralisation and alteration systems at the Nevera Prospect. NEV027 is located approximately 200 metres south of the existing announced mixing zone resource boundary. Gold mineralisation is now seen some 500m lower than previous drilling.
Base Metal Mineralisation Analysis
Very strong base metal and silver mineralisation were intersected in the hole with several zones assaying over 0.50% of combined lead (Pb) and zinc (Zn): a table detailing these intercepts is included below as Table 2.
As noted in an earlier release to the ASX, NEV027 intersected the top of a porphyry intrusion at a depth of 1046m, which is considered to be an apophysis of the main deep major intrusion responsible for baking the Chim Formation shales intersected in earlier drilling. This porphyry has proved to be copper bearing with elevated zones of copper geochemistry intersected, with a 68m zone within and immediately adjacent to the porphyry (from 1,036m to 1,104m EOH) grading 0.08% Cu (800 ppm Cu). This is highly encouraging as NEV027 only just intersected the top of the intrusive complex with several large Chim Formation clasts (fragments) incorporated within the porphyry groundmass (as xenoliths). The copper grades in the intrusion are more than double the grades above the intrusion. The Company considers that NEV030 which is designed to drill an additional 200m deeper into the porphyry has the potential to intersect higher Cu grades with depth.
GOA Exploration director Peter Macnab stated “the extent of the mineralisation and alteration seen in NEV027 further confirms our belief that the mineralisation system we are seeing at Nevera is very extensive and we are making significant steps in our understanding of the geology of this prospect which will aid us with our future drilling programs”.
He added “The mineralising system we are seeing at Nevera is very similar to prototype porphyry Cu and Cu/Au systems seen around the world with a large central intrusion surrounded by variably mineralized multiple porphyry apophyses, sitting at the base of a large mineralised hypothermal system with multiple mineral deposits, and this bodes well for future drilling”.
NEV030 (the second planned deep hole) is currently at a depth of 501.40m with drilling set to resume early next week. NEV031 drilled to test the northeast extent of the mixing zone was completed prior to the Christmas break to a depth of 602.90m. Results are due out late January early February 2012.
SGS now advise that the first batch of samples from NEV029 have reached the laboratory in Townsville and results from the entire hole will now be due out in early to mid-January.