Nexus Minerals Limited announced positive results from its Bethanga porphyry Cu-Au fertility assessment study. The study was undertaken over an 18-month period, on the Company's Bethanga porphyry Cu-Au project, 50km east of Albury-Wodonga, and 350km northeast of Melbourne, Victoria. Study work included regional and detailed geophysical surveys, soil sampling surveys, rock lithogeochemistry and detailed geological mapping programs. The Bethanga porphyry Cu-Au project lies within the East Lachlan Fold Belt (ELFB). This belt has an endowment of more than 13 million tonnes of copper and 80 million ounces of gold. It hosts the Tier 1 Newcrest Cadia - Ridgeway deposits that represent some of the world's most profitable producers. In addition, the ELFB hosts the long-life mining copper-gold operations at Northparkes and Cowal. The Bethanga project lies in a unique tectonic setting and has recently been recognised by the Geological Survey of Victoria as a region highly prospective for porphyry copper-gold style mineralisation. Typical Cu-Au porphyries display a magnetic "potassic zone" at the core of the system containing alteration minerals magnetite, biotite and k-feldspar. This potassic zone is surrounded by the non-magnetic "phyllic zone" containing quartz, sericite/white mica (illite /muscovite) and pyrite, extending outwards to the "propylitic zone" containing chlorite, epidote and carbonate. This zonation can result in a magnetic response comprising a magnetic high (potassic zone) surrounded by a magnetic low (phyllic zone). Geophysics: The publicly available aeromagnetic data sets highlighted an area of 3km x 1.5km that appear to represent a large scale magnetic intrusive complex. Magnetic anomalies are commonly associated with mineralised porphyries as they represent the core "potassic zone" and hence provide excellent targets for drill testing. The anomalous area identified from regional aeromagnetics was subjected to a detailed ground magnetics survey which has confirmed this zonation in magnetic response. Detailed geological mapping over the area has identified a multiple phase Granodiorite-Diorite (highly magnetic) intrusive complex. Magnetic susceptibility readings of the outcropping rock units have confirmed the diorite intrusion as the source of the magnetic high. The coincidence of the magnetic susceptibilities in the Granodiorite-Diorite (highly magnetic) intrusive complex over the aeromagnetic and ground magnetic data suggests that they are related to a larger
intrusion at depth. Additionally, rock chip samples from the magnetic low area surrounding the magnetic high, exhibit Na loss attributed to feldspar destructive hydrothermal alteration and the formation of well crystallised white mica (illite /muscovite) indicative of phyllic alteration (Phyllic Zone). Geology and Rock Chip Geochemistry: Geological mapping and associated collection of rock chips has shown a clear zonation of rock types, and
associated prospectivity, from north to south of the project area. In the north the Bethanga granitic gneiss dominates. Gneiss is a foliated metamorphic rock identified by its bands of varying mineral composition. The mafic minerals show a preferred orientation that parallels the overall banding in the rock. Intense heat and pressure have metamorphosed the original granite into the gneiss. Moving south the rocks transition into more granitic composition and then granite porphyry. The hornblende-bearing granodiorite ­ diorite (magnetic) intrusives are seen in the south of the project area, in
addition there are localised high silica and altered breccia units. The rock chip geochemistry also shows a zonation from north to south, with gold dominating the northern area, coincident with old historic gold workings of high-grade narrow veins. Copper dominates the central area
and this is coincident with old historic copper workings again of high-grade narrow veins. In the south of the project area where the intrusive rock units are exposed a multi-element signature is seen. Elevated porphyry copper pathfinder elements: Cu, As, Sb, Bi, Te, Ag and Li occur in and around the intrusive complex, with the breccias having distinctive high silica compositions accompanied by elevated As and Sb. A high proportion of the whole rock samples from this area plot in the prospective filed for western Pacific porphyry Cu systems. Many of the samples are moderately oxidized based on Fe2O3/FeO ratios and are poorly fractionated. 33 samples were analysed with SWIR (short wave infrared) and VNIR (visible to near infrared radiation) to assist in mineralogy and alteration assemblage identification. The samples were from the southern part of the project area. The granite porphyry and breccia show varying degrees of Na loss attributed to feldspar destructive hydrothermal alteration and the formation of well crystallised white mica (illite /muscovite) indicative of phyllic alteration (Phyllic Zone). Diorite samples also contain biotite that is partially chloritised (consistent with propylitic alteration). In addition to the above positive factors, detailed plots of V/Sc vs Sc suggest the granodiorite-diorite samples are prospective for porphyry Cu systems The relationship reflects mineral fractionation in response to the oxidation state of the magma. The granodiorite-diorite samples have also been classified according to their Fe2O3/FeO ratio as a more direct indicator of oxidation class. The samples plotted on the fertility plot show
samples falling within the field of ore-forming porphyry Cu intrusions from the western Pacific region in terms of their hydrous nature, with many samples having been derived from moderately to strongly oxidized magmas. The oxidized nature of some diorite samples is also indicated by the presence of accessory magnetite, and the presence of hornblende also attests to the hydrous nature of these rocks. These rocks also plot as poorly
fractionated, with Rb/Sr ratios of <1, and some are moderately evolved based on a K/Rb ratio between 200 and 300.