Borroloola West, Northern Territory - Copper/Zinc Joint Venture with Sandfire Resources NL (Pacifico 51% Sandfire 49%)
The BWJV consists of 12 exploration licences and 1 mining licence (1,817 km2), and lies west and northwest of the world class McArthur River zinc-lead mine and Rox Resources’ zinc-lead resource at the world class Teena deposit (figure 1). The parties to the BWJV are 51% Pacifico Minerals Limited ("Pacifico" or "Company") (ASX code: PMY) and 49% Sandfire Resources NL ("Sandfire") (ASX code: SFR).
Sandfire is supportive of the exploration program and will continue to contribute its 49% share of all exploration costs. Diamond and RC drilling is planned during the 2017 field season to test the Coppermine Creek (copper-cobalt-silver), Mariner (zinc-lead) and Berjaya (zinc-lead) prospects. Preparatory work, including a potential ground EM survey, are planned to commence when the Northern Territory period of heavy rain finishes. Pacifico's reverse circulation drilling program in 2016 confirmed the continuity of stratabound copper mineralisation of Mount Isa Copper/Nifty deposit style at Coppermine Creek, with an intersection of 10m of 1.3% Cu in CCR08 (see ASX announcement 23 November 2016).
At the Mariner Prospect, the 2016 drilling intersected geochemically high lead values (21m of 1.0% Pb in MNR01: see ASX announcement 23 November 2016), indicating possible proximal hydromorphic dispersion from significant zinc-lead mineralisation in the underlying McArthur Group sediments.
Figure 1: Borroloola West Project Tenements (Pacifico 51%, and Sandfire 49%) and location of prospects
Coppermine Creek (copper-cobalt, silver)
The thickness, continuity and style of the copper (as well as cobalt and silver) mineralisation at Coppermine Creek are impressive. The mineralised zone, is spatially controlled by an evaporite horizon (figure 4) extending south and dipping gently from the copper mineralised at the Gordons Fault (figures 3 and 4).
The outcrop length of the mineralisation is 700m (figure 3). Applying a 0.3% Cu grade cut off, the average intersection thickness of the 12 holes is 9m, with a length weighted average intersection grade of 1.0% Cu (table 1). The primary mineralisation consists mostly of veins, stringers and disseminations of chalcopyrite, with only minor pyrite (figure 2), indicating relatively simple metallurgy.
Figure 2: Drill Core CCD03 - semi-massive chalcopyrite bands
Drilling also indicates there is potential for significant tonnage of near surface oxidised copper mineralisation (chalcocite and malachite) extending down to approximately 50m depth that may augment the oxidised copper minerlisation previously drilled out at the Lorella Prospect, 30 kilometres north of Coppermine Creek (figure 1). Pacifico will investigate its potential for on-site leaching. In the high carbonate host rocks, an alternative leaching method (eg. Glycine) would be evaluated in order to avoid excessive acid consumption.
Conductivity measurements of mineralised core containing semi-massive sulphides intersected in holes CCD02 and CCD03 (figure 4) as well as unmineralised drill core, will get underway in early 2017 and if the results are positive, ground EM lines will be conducted south of the Gordons Fault (figure 3) to further define the diamond drill targets below 150m to 400m of the overlying stratigraphy.
|Drill Hole Number||From (m)||To (m)||Intersection Length (m)||Cu %||Co ppm|
Table 1: Pacifico (CC series) and previous explorer's drill intersections of copper and cobalt through the stratabound evaporite zone, using a cut-off of 0.3% Cu
na = not analysed
MIM = Mount Isa Mines Ltd
BHP = BHP Exploration Pty Ltd
Carrington = Carrington Mines Ltd
Figure 3: Coppermine Creek Prospect – Geological plan showing projected drill hole traces, copper mineralisation and planned extent of ground EM survey
Figure 4: Coppermine Creek Prospect – north-south section showing probable extension of stratabound copper mineralisation southwards
Four RC holes were drilled by Pacifico during the 2016 field season (MNR01 to MNR04: see ASX announcement 23 November 2016). The drilling demonstrates that oxidised lead mineralisation occurs at the base of the Roper Group. The basal unit of the Roper Group consists of sandstone, siltstone and chert breccia fragments in a clayey matrix.
|Hole ID||From (m)||To (m)||Length||Pb|
Table 2: Lead intersections at Mariner
The lead mineralised zones are also slightly anomalous in zinc (up to 549ppm Zn over 1m interval). As the Roper Group contains no known primary mineralisation whatsoever regionally, it is likely that the lead and zinc originate from base metal mineralisation in the underlying McArthur Group and has moved by hydromorphic dispersion along the contact unconformity (figure 5).
Once the wet season is over, Pacifico's exploration team will carry out geological mapping and portable X-Ray Fluorescence ("pXRF") rock chip geochemistry over the area to the north-west of existing drill collars (figure 6), where the potential base metal mineralisation could lie, to better define the target zone, and culminating in diamond drilling to test the McArthur Group for sediment hosted, stratabound, zinc-lead mineralisation.
Figure 5: Section east-west through MNR01, also showing previous MIM percussion holes RDH02 and RDH03
Figure 6: Mariner Prospect – Updated interpreted geological plan showing historial and Pacifico (MNR series) drill collars
The Berjaya tenement covers several kilometers of suboutcropping, gently dipping Barney Creek Formation (figure 7) which is the host to the McArthur River and Teena zinc-lead deposits. Reverse circulation drilling by Pacifico in 2016 intersected oxidised Barney Creek Formation in drill hole BJR01 (see ASX announcement 23 November 2016). Diamond drilling is planned to test a flat lying low resistivity zone in VTEM flown by Pacifico, 1km to the north of BJR01.
When the Northern Territory period of heavy rain finishes, Pacifico's exploration team will be carrying out geological mapping and geochemical rock chip sampling to further refine the position of the planned diamond drill hole.
Figure 7: Berjaya EL28508 – Geology and RC drill hole collars
Four Mile (zinc-lead)
Five RC holes FMR01 to 05 were drilled at Four Mile (figure 8). The section (figure 9) shows the beds dipping at about 25 deg overall, to the west.
There is very fine disseminated pyrite throughout the Barney Creek Formation carbonaceous siltstone. Sulphur values indicate an average of about 0.5 volume % pyrite. This increases to over 1% and up to 4% pyrite in an upper and lower sulphidic zone, both several meters thick (figures 8) but contain no significant associated base metals. Below the upper sulphidic zone in FMR05 there are several meters of elevated Pb, from 300ppm to 900ppm Pb, associated with thin dolomite veinlets. This may be reflecting the vicinity of the potentially mineralising NE trending fault (figure 9).
This western section of the Barney Creek Formation tested at Four Mile is considered in a regional context as prospective as those parts around the McArthur River Mine. More detailed geochemistry of the sulphide rich zones is being undertaken that may indicate the vicinity of, or vectors to SHMS mineralisation.
Figure 8: Four Mile Prospect – RC drill collars and reinterpreted geology
Figure 9: Four Mile Prospect - East-west Section through FMR05 and FMR04
One RC hole was drilled at the Johnstons Prospect (JTR01), and 3 RC holes (CCR05, 06, 07) were drilled to test a gossanous breccia 2km east of the Coppermine Creek prospect. No significant results were obtained indicating that mineralisation is discontinuous and patchy.