Nexus Minerals Limited Announces Positive Results from its Bethanga Porphyry Cu-Au Fertility Assessment Study
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.