Final report Plenty River Project EL 23792 and EL 25007 for the period 1 November 2005 to 119 December 2011

Abstract

The Plenty River Project (EL 23792 and EL 25007) was a greenfields exploration project located in central south-eastern Northern Territory and was targeting diamonds, and base metal mineralisation below the Cretaceous (Eromanga Basin) sediments. Initial exploration work comprised loam sampling and near surface drilling for kimberlite pipes undertaken under a joint venture between AusQuest and Rio Tinto Exploration Ltd from 2005 - 2006. No diamonds or KIM were recovered. AusQuest acquired detailed geophysical data (gravity) that suggested a coincident gravity /magnetic target below the Cretaceous sediments may have potential for IOCG style mineralisation. The original exploration model for the Plenty River Project was based on comparisons with the Prominent Hill style deposit located in South Australia which is characterised by a low tenor gravity response and a semicoincident magnetic anomaly reflecting the presence of significant quantities of hematite mineralisation (alteration). Drilling in 2009, four holes totalling 1470.18 m, under the first NTG Drilling Collaboration Program (Sherington et al 2009) did not confirm hematite alteration, but did locate a sedimentary basin with interlayered mafic sills. A second phase of ground EM surveys was completed in 2010 and this indicated a potential conductive geophysical target at depth and offset from the 2009 drilling target. A possible basin (base metal) style mineralisation model was inferred and 3 holes were planned to test the target. AusQuest applied for additional funding under the Northern Territory Government Drilling Collaborations Programme in May 2011 and received approval July 2011. Two diamond holes (11CPD004 and 005) totalling 1305.5 m were completed and intersected a thick sequence of sulphidic (pyrrhotite) laminated sediments with interbedded felsic volcaniclastics and interlayered mafic sills. Physical property measurements on core confirmed the magnetic anomaly is caused by the pyrrhotite mineralisation and the gravity response is due to a thick section of gabbro/dolerite in the core of a synclinal structure. The presence of graphite in the laminated sediments is the most likely cause of the conductive response. Weakly elevated base metal values were encountered within the sedimentary package but no ore grade intersections were returned, and the tenements were subsequently surrendered.