The Western Group of Tenements
(EL 2401, ELA 2468)
These tenements cover the Amanab Block, a segment of metamorphic basement located near the northern edge of the New Guinea Mobile Belt. The presence of very old (Permian age) intrusive rocks in float indicate the block may be underlain by a fragment of Australian continental crust. If so, this implies a thicker crust and increased potential for economic gold-copper mineralization.
The basement rocks consist of Cretaceous to Eocene phyllites, slates, schists, quartzites, limestones and volcanics which are intruded by numerous bodies of weakly metamorphosed gabbro, diorite and granodiorite. The meta-intrusive rocks are thought to be the primary source of the alluvial gold. Parts of the basement are overlain by limestone, sandstone, siltstone and conglomerate.
Alluvial gold is widespread in the Amanab Block and small-scale artisinal alluvial mining has been undertaken more or less continuously at various locations since the 1940's. In the mid 1970's production was reported to be 730g gold per month, increasing to 2500-3000g per month by 1988. Eighty percent of the production came from the Yup River drainage area, the remainder from other areas.
Localised mineral exploration has been undertaken since 1970 by various companies targeting both specific alluvial gold deposits and the bedrock sources of the alluvial gold. Aerial geophysics were utilized in some areas but none of these companies completed fully integrated comprehensive surveys combining geology & the latest techniques of broad-scale regional geophysics (ZTEM eg) coupled with advanced recently available high resolution imaging tools for targeted anomalies such as 3D IP, drone magnetics & LIDAR, deep reading GPR & 3D IP to accurately define drilling targets and no drilling has been undertaken in the area other than some alluvial sampling in very localised areas characterised by artisanal workings in easily accessible areas.
Collectively the historical results are very encouraging and show the following:
- The presence of regionally important very large scale NE-trending arc normal transfer and NW-trending arc-parallel structures, these represent structures with a high potential to have acted as conduits for mineralising fluids and for the emplacement of porphyry copper/gold intrusions as well as TAG & epithermal gold deposits .
- The basement hosts a number of magnetic anomalies interpreted as plug-like bodies (from historical geophysical data).
- Carbonaceous phyllite and schist are present in the metamorphic basement (carbon helps to fix gold mineralization in these rock types).
- Epithermal vein quartz has been found in float and epithermal quartz-sulphide veins associated with sericite alteration have been found in outcrop.
- There is widespread anomalous gold in stream sediment samples with highly anomalous values greater than 1.0 g/t gold very common. The highest reported values were 107 g/t gold in stream silt samples and 58 g/t gold in panned concentrate samples. This indicates that both coarse and fine alluvial gold is present.
- Multiple target areas have been defined for follow up exploration, none of which have been fully evaluated.
- One high tenor gold target was reported with a strike length of more than 5km and highest gold values of 13.8 g/t gold in soil and 39 g/t gold in rock chips.
- Textures in some alluvial gold grains indicate a nearby hard rock source of the gold.
One previous explorer (Harmony Gold, 2010) concluded that "the area is very prospective for epithermal and porphyry style gold and copper ore bodies lying within the New Guinea Mobile Belt and the Amanab alluvial goldfield".
The Western Group of tenements area is highly prospective and underexplored. The widespread occurrences of alluvial gold and multiple targets over a large area indicate a strategy to utilize regional and focused localised airborne geophysics in the initial exploration phase is the right approach.