Large Altered Porphyry System with Enhanced Copper-Gold Potential Confirmed at Nankivel
The newly interpreted porphyry core has a diameter of at least 800m under less than 20m of cover and is located 4km southeast of the 42Moz Paris Silver Project. Both prospects are within the Company's 100% held Peterlumbo tenement underlain by pastoral leases near Kimba on the northern Eyre Peninsula of South Australia.
The four inclined holes were drilled over the past month into IP chargeability targets to follow-up 2016 scout drilling that intersected the interpreted rim of a porphyry system which Investigator has predicted as a new deposit style in South Australia.
The new inclined holes, averaging around 400m downhole depth, intersected potassic-altered monzodiorite, a prospective porphyry rock, from as shallow as 4m under surface soil and gravel cover. The drill core variously demonstrates typical porphyry alteration, brecciation, veining and zonation. Disseminated and vein-hosted zinc and lead sulphides graduate to copper sulphide (chalcopyrite) at depth. An overprinting phase of intrusion, alteration, brecciation and mineralisation has demonstrated the potential for younger porphyry deposits and high-grade epithermal deposits within the Nankivel system.
Managing Director, John Anderson, said he took great pleasure in announcing the results from the broad-spaced drill tests. "With coarse first-pass drilling mostly on a 400m spacing, Investigator Resources has established beyond any doubt the presence of a large, very prospective copper-mineralised porphyry system. We consider Nankivel is the same age as Olympic Dam, making it one of the oldest geologically in the world with potential for world-class copper discoveries.
"The discovery of an economic copper-gold porphyry at Nankivel or nearer to Paris would be transformational for Investigator. Major companies are scouring the world for such opportunities, mostly at depth near known deposits in established porphyry belts around the Pacific. At Paris-Nankivel, Investigator has targets starting just below the surface in a new epithermal-porphyry province associated with the Olympic Dam mineralising mega-event, with the bonus of being in an OECD country."
Mr Anderson said that the levels of visible chalcopyrite were not yet expected to achieve economic grades, but there was excellent potential within such an extensive copper mineralised system for copper-rich shells between, beneath and beyond the first-pass holes. The geology and amount of sulphide were also prospective for associated gold, which would be tested with the first batch of assays, expected in early May.
He said the alteration also observed in the drill core strongly inferred potential for shallow, high-grade gold-silver-copper deposits, which are common over the top of porphyry systems. Indications of such a high-sulphidation target were intersected as high-level alteration and veins in the collars of two adjacent holes and are supported by an adjacent 400m long geophysical conductor.
"The new targeting parameters learned from the drilling greatly enhanced the exploration potential of the 50km2 Paris-Nankivel field, for both shallow high-grade silver and gold targets analogous to the Paris silver project, and multiple targets for world-class porphyry copper-gold deposits.
"Investigator has the first-mover advantage of initial discovery and development opportunities at Paris-Nankivel. We acknowledge the assistance of the State Government's collaborative drill program in making the breakthrough for South Australia's mineral potential," Mr Anderson said.
A 1,632m drilling program of four diamond core holes PPDH154-157 was completed at Nankivel in March-April. The holes followed 2015 and 2016 scout drilling that demonstrated a propylitic rim to a predicted copper-gold prospective potassic core of a porphyry system (Figure 1, see link below).
An undrilled magnetic low of 1.5km by 800m dimensions was interpreted as the demagnetised porphyry target. A broad Induced Polarisation (IP) survey was undertaken over the target area on 400m spaced survey lines in late 2016. The new drilling tested a selection of IP chargeability anomalies also on the broad 400m spacing (Figure 3, see link below). The last hole PPDH157 was drilled 100m behind PPDH155 to follow up positive results with structural and deeper data.
Positive visual outcomes
All four drill holes intersected potassic-altered porphyritic monzodiorite over the drilled area with fracturing, veining and multiple intrusives expected in a mineralised porphyry system (Photos pages 2 & 5, see link below). The potassic alteration variously shows the minerals expected in a porphyry - potash feldspar, biotite, magnetite and tourmaline. Hole PPDH155 intersected an intact zoning pattern typical of a porphyry (Figure 2, see link below) ranging from 30m of shallow advanced argillic alteration (kaolinite, illite, topaz, fluorite, pyrite and silver and copper chlorides), above 200m of intense phyllic alteration and brecciation (silica sericite pyrite carbonate fluorite lead and zinc sulphides), subsequently entering the potassic altered monzodiorite. A similar vertical zonation is seen in the sulphide mineralogy from trace to 1% galena (lead sulphide) and sphalerite (zinc sulphide) transitioning to chalcopyrite (copper sulphide) about 200m below the surface.
Hole PPDH157 on the same cross section confirmed the zoning pattern (Figure 2). It only intersected a metre of argillic clay under about 15m of transported cover, then intersected potassic zones either side of the phyllic zone that contained steep dipping carbonate-pyrite-fluorite-chalcopyrite-veins at the interpreted position of the central mineralising structure. Fluorine-bearing minerals fluorite and topaz are common as prospective mineralisation indicators in and around the structure. The structure is interpreted to progress vertically from deeper carbonate-pyrite-fluorite-chalcopyrite brecciated veins in PPDH157 to mid-level chalcedonic breccias in PPDH155, then to the fluorite and topaz in the upper advanced argillic cap. The prospective structure is interpreted as projecting in plan from the advanced argillic and quartz vein outcrops on Nankivel Hill westerly past the strongly pyritic intersection in PPRC404, then through the breccias, veins and alteration of PPDH155/7 for a distance of at least 1.5km.
The copper mineralisation is estimated to be low to modest visually and is not expected to produce significant grades. The mineral zoning suggests that any higher-grade copper shell to a modelled late intrusive is at least 500m below the surface beneath current drilling. Although deep, there is alteration and intrusive evidence for multiple porphyry events at Nankivel that implies shallower ("telescoped") porphyry deposits.
Samples for PPDH155 have been submitted for assay with results expected mid-May. Cutting of the assay samples for the remaining holes is about to start.
The assays will also be used to assess vertical and lateral vectors to proximal porphyry and epithermal targets by the comparison of the multi-element data between holes.
Further discovery opportunities
The drilling at Nankivel has opened up the following exploration opportunities:-
Nankivel porphyry prospectivity
The discovery of potassic-altered porphyry with copper mineralisation, albeit at modest visual levels to date, over such a broad lightly drilled area offers good potential for shallower copper-rich shells around smaller late porphyry intrusives between or below the current drill holes at Nankivel.
High sulphidation gold-copper deposits
The advanced argillic alteration preserved near the surface implies potential for shallow high-grade gold and copper deposits within the Nankivel system. Such a potential high-sulphidation target is delineated as a 400m long conductive feature by a single airborne VTEM (Versatile Time Domain Electromagnetic) line flown across Nankivel by CSIRO for hydrological studies (Figures 1 & 3). This possible conductor lies along the interpreted western projection of the central structure and is adjacent to limited kaolinite gossan (oxidised sulphides) veins around 50m down hole PPDH156 that was drilled away from the target (Figure 1) into an alternative IP chargeability target.
The conductive feature is about 100m thick and flat-dipping to the west with depth to the bottom of the conductor ranging from 80m to 140m below the surface. This coincides with a similar deepening IP conductor in the IP data that may represent a one kilometre extension of the advanced argillic alteration intersected in PPDH155. This is shown as the yellow zone in Figure 1 and is interpreted in the IP conductivity data to deepen from 50m at PPDH155 to 200m deep at the western extension. The scenario is similar to Paris and may also follow the unconformity boundary between volcanics and basement as seen around Nankivel Hill.
Other silver, copper and gold targets within the Paris-Nankivel epithermal-porphyry complex
Figure 4 (see link below) shows a regional image of the magnetics overlain by the VTEM flight lines. It is noted that most of the known prospects show associated VTEM anomalies where crossed by the flight lines. The VTEM responses at Paris, previously interpreted as due to the graphitic wallrocks, requires review.
Figure 5 (see link below) shows the targeting model for the Paris-Nankivel complex. The interpreted prospective connecting structures are based on geological, geophysical and geochemical factors and is an example of Investigator's use of integrated techniques for targeting. The distribution of low-level molybdenum is a good example of how Investigator's extensive research database is being used to apply pathfinder geochemistry to mapping prospective fairways and clusters of mineralisation.
In addition to Nankivel, three other areas are selected as having similar magnetic and molybdenum signatures with potential to be prospective porphyry centres - Nankivel Southwest, Nankivel East and Helen. The Nankivel high-sulphidation target is shown on Figure 5 connecting Nankivel Hill with Nankivel Southwest. Nankivel West extending from the Nankivel porphyry towards Paris is seen as another priority shallow gold target.
The Alexander and Ares silver targets will also be reviewed.
The entire area of Figure 5 has been heritage surveyed. Hills generally corresponding with silicified volcanics such as Nankivel Hill are now nominated as unavailable for drill access. Clearance under a prior heritage survey permitted drilling at Nankivel Hill in the past. All the nominated targets except Nankivel Hill are cleared for drill access.
For the immediate Nankivel targeting, assays are awaited for the first batch of samples submitted for PPDH155. All the core is in Adelaide and cutting of assay samples for the remainder of the holes will resume soon, supported by petrological work including further spectral mineralogy.
Two levels of wider exploration work will proceed:-
1) Assessing the new and revised shallow silver and gold targets for potential synergies with the silver project at Paris. Priority will be given to advancing the Nankivel high-sulphidation target.
2) Seeking shallow tops to mineralised copper shells within the four nominated porphyry target areas.
Both strategies will benefit from assessment of the Company's drill geochemistry datasets with different elements being applicable to mapping structural connectors and porphyry versus epithermal signatures. This work is on-going.
Review of the VTEM data along with the undrilled Nankivel IP anomalies will be undertaken. Expanded IP and electromagnetic (EM) ground surveying will then be considered for both target strategies.
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About Investigator Resources Ltd
Investigator Resources Limited (ASX:IVR) is a metals explorer with a focus on the opportunities for greenfields silver-lead, copper-gold and nickel discoveries offered by the emerging minerals frontier of the southern Gawler Craton on South Australia’s northern Eyre Peninsula.
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