Trundle
In January 2008, Calibre Mining Corp, through its wholly-owned subsidiary Calibre Mining (Australia) Pty Ltd, entered into an agreement with Western Plains Resources Ltd (ASX:WPR) to explore the Trundle property. Calibre can earn a 70% interest in the Property by completing AUS $3.0 million in exploration expenditures over a three year period, including a minimum expenditure of AUS $600,000 in the first year. The Company will have the option to acquire an additional 20% interest (for a total of 90%) by funding and completing a Feasibility Study. Calibre is the operator of the Property.
LOCATION AND GEOLOGICAL SETTING
Trundle is located approximately 355 km west-northwest of Sydney and 300 km northwest of Canberra in NSW. The 78 square kilometre tenement covers a window of largely overburden-covered Ordovician volcanic rocks (Raggatt Volcanics) that are considered to be a rifted portion of Goonumbla Volcanic Complex that hosts the Northparkes copper-gold district some 25 km to the east.
Trundle contains widespread evidence of porphyry and skarn-style copper-gold mineralization associated with several discrete intrusive centers. Historical RAB and air core drilling on four of these centers identified bedrock copper and gold mineralization coincident with airborne magnetic highs. Limited RC drilling by Newcrest around the periphery of three of these centers -- Mordialloc, Bloomfield's and Copper Hill confirmed the presence of porphyry-style alteration and mineralization however drilling penetrated to only shallow depths.
2008 EXPLORATION PROGRAM
Calibre's 2008 exploration program focuses on the northern targets: Mordialloc, Bloomfield's and Yarrabandai. A 3,700 metre diamond drilling program has been designed to test these targets at depth (>500m) for high grade porphyry Cu-Au mineralization. Drill holes have been placed to test magnetic features consistent with structures and magnetite bearing potassic alteration at depth, as well as anomalous copper and gold bedrock geochemistry from historical RAB and air core drilling. In covered areas, the targets have been further defined through the systematic application of partial leach geochemistry and soil pH measurements.
REGIONAL GEOLOGY
The tenement covers a "window" of Late Ordovician-age Raggatt Volcanics, which are widely regarded as stratigraphic equivalent of the late Ordovician (450 Ma.) Goonumbla Volcanics. The high-grade Northparkes porphyry copper-gold deposits, located 25 kilometres due east is hosted in the Goonumbla Volcanics. Trundle is separated from the Northparkes district by the Tullamore Syncline; a north-south trending Devonian rift. Interpretation of aeromagnetic data (Figure 2 - Regional Setting Map) suggests that the Raggatt Volcanics may have originally been part of a large volcanic complex or caldera-like feature that was subsequently dismembered by the development of the rift.
Trundle lies within the west-northwest trending Lachlan River Lineament. This interpreted transform structure is considered to have acted as an important control on late Ordovician magmatism and on the emplacement of mineralized porphyry centres in the region (e.g. Cadia-Ridgeway, Northparkes, Copper Hill and Cargo).
The late Ordovician Raggatt Volcanics at Trundle consist of a co-magmatic suite of andesite flows, pyroclastics and volcaniclastic sediments with minor carbonate-rich units, including limestone. These rocks are intruded by hypabyssal sub-volcanic stocks that range in composition from diorite to quartz monzonite. The Raggatt Volcanics are high-potassic calc-alkaline to shoshonitic in composition. A zone of pyroclastics and volcaniclastic sediments in the central part of the project area is possibly of Upper Silurian age, and may unconformably overly the Raggatt Volcanics. Sediments and minor acid volcanics of the Lower Devonian Derriwong Beds unconformably overly the Raggatt Volcanics on the western side of the project area (Figure 3 - Simplified Geology Map).
PREVIOUS WORK AND TARGETS
Previous work on the tenement by WPR, Placer Pacific Ltd., Newcrest, PlatSearch NL and Lachlan Resources NL identified a number of Cu-Au targets representing both skarn and porphyry styles of mineralization. Most historic work involved grid RAB and Aircore drilling for geochemical samples and mapping purposes.
A number of highly prospective copper-gold porphyry targets are known on the tenement (Figure 4 - Targets Map). They are defined on the basis of copper and gold geochemical results from the historical RAB and Air Core drilling as well as airborne magnetics. Several targets bear striking similarities to the Endeavour 22, 27 and Veedas porphyry deposits at Northparkes (Figure 5 - Northern Targets Map), which have a characteristic 'bulls eye' magnetic low or high patterns with coincidently anomalous copper and gold geochemistry in RAB drilling. This pattern can be seen at Bloomfield, Mordialloc, and Copper Hill East targets. In addition, there are several other significant copper-gold anomalies that remain poorly drilled or undrilled.
EXPLORATION POTENTIAL
North Tenement Area
Calibre considers the Trundle project to have excellent potential for the discovery of one or more economic porphyry gold-copper deposit of a style similar to the known deposits in the Northparkes district. Top priority targets in the northern part of the tenement include the Mordialloc, Yarrabandai, and Bloomfield (Figure 3 - Simplified Geology Map).
Mordialloc consists of a 1,300 metre diameter, circular magnetic high with coincidently anomalous copper (>500 ppm) and gold (> 0.2 ppm) geochemistry (from RAB drilling - Figure 4 - Targets Map). Geology determined from the RAB drilling and from a few shallow RC holes on the edges of the target, show that the feature corresponds with a northeast elongated mafic monzonite porphyry intrusion; a favourable rock type for mineralization at Northparkes.
Yarrabandai (Figure 4 - Targets Map) is also underlain by mafic monzonite. This target consists of a northeast trending zone approximately 600m long of strongly anomalous gold (>0.20 ppm) and copper (>400 ppm) geochemistry forming a tail off the southwest end of Mordialloc. Unlike Mordialloc, Yarrabandai coincides with a diffuse magnetic low. Neither target has been effectively drill tested for porphyry style mineralization.
Bloomfield (Figure 6 - Bloomfield Target Map) is a similar style of target to Mordialloc. Located 2 km southeast of Mordialloc, it consists of a discrete circular magnetic high, approximately 1,100 metres in diameter, with a subtle central low. Historic RAB drilling over the magnetic feature shows the area is broadly anomalous in copper and gold with widespread values of >200 ppm and >0.1 ppm respectively. Geological mapping by Western Plains identified a northeast trending mafic monzonite-diorite intrusion hosted by andesitic volcanics, coincident with the magnetic anomaly. Patchy zones of weak quartz-sericite-pyrite and propylitic alteration were defined mostly within the volcanics and minor potassic alteration was noted in a few holes drilled into the intrusion. Two fences of RC holes drilled by Newcrest tested the outer edges of the magnetic feature sub-parallel to the long axis of the mapped intrusion. They encountered only low tenor copper and gold mineralization. No drilling has been done into the core of the anomaly to test for high-grade Endeavour 26 style mineralization.
Copper Hill Area
Important exploration potential also exists in the Copper Hill area in the southeast part of the tenement. Old workings at Copper Hill (Figure 7 - Copper Hill Map) reportedly produced 380 ounces of gold from a shallow open pit and glory hole excavated on an oxidized outcrop of an irregular shaped raft of skarn. This body of skarn mineralization is contained within a large intrusive complex composed of mafic monzonite and diorite in the southeastern part of the tenement.
Initial prospect development comprised grid-based RAB bedrock geochemistry, with the results defining significant bedrock gold and copper anomalies up to 250 metres long and 20 to 100 metres wide. These anomalies were subsequently tested with percussion drilling of 12 holes (936 metres) by two companies; Placer and Newcrest. Several broad zones of low-grade gold mineralization contained within a west-dipping skarn body were intersected, the best being 39 metres at 0.55 g/t gold in hole PCH-10 and 35 metres at 0.56 g/t gold in PCH-11. Narrow high-grade zones were also intersected in hole PPT3 (9 metres at 2.2 g/t gold, 0.49% copper) and hole PCH-9 (4 metres at 3.2 g/t gold).
More recent work includes deeper drilling of 812 metres in two diamond holes (TD-01 and TD-02) and 781 metres in five inclined RCP holes (TD-03, TD-21, TD-22 and TD-23). As with earlier drilling, TD-01 also intersected broad intervals of low grade gold mineralization associated with fracture-controlled pyrite veining in a mixed zone of propylitically altered andesite and intrusive rocks. The most significant results were 151 metres at 0.23 g/t gold from 20 metres down hole and 60 metres at 0.88 g/t gold from 200 metres. The hole passed through a west dipping thrust fault into Lower Devonian sediments at 345 metres. Other significant results include TD-22 (68 metres at 0.13 g/t gold) and TD-23 (48 metres at 0.14 g/t gold).
A regional aircore hole TR-143 intersected 11 metres at 1.2 g/t gold and 0.36% copper approximately 500 metres north-west of the Copper Hill workings. The mineralisation is associated with oxidized skarn. An adjacent small magnetic high was tested by hole TD-46 and intersected 10 metres at 0.58 g/t gold in diorite with weak propylitic alteration.
Copper Hill East Prospect
Early grid-based RAB sampling at Copper Hill East delineated a 550-metre long bedrock gold anomaly (>0.4ppm to 3.12 ppm) with associated minor copper (>100 ppm). The anomaly is situated approximately 500 metres north-east of the Copper Hill workings as shown in Figure 7 - Copper Hill Map. The southern part of the anomaly has been tested by a short diamond core tail in hole LDDH-1 that intersected 6.2 metres at 1.9 g/t gold. Diamond hole CHEP-1 also made an encouraging intersection of 17 metres at 0.67 g/t gold.
Mineralisation at this locality is associated with quartz-sericite-pyrite alteration in andesite. This style of alteration is present in the outer zones of the Northparkes porphyry systems. The depth potential at Copper Hill East may be limited by the proximity to the low-angle thrust fault; however, a significant strike length of the anomaly remains untested.
Dunn's Prospect
Bedrock geochemical sampling by Geopeko, delineated several erratic weak, gold-copper anomalies in an area surrounding scattered old shallow workings in contact skarns at Dunn's (Figure 7 - Copper Hill Map). The best anomalies were tested with shallow percussion holes; the most significant intersections were from PPT-8 (10 metres at 1.99 g/t gold, 0.13% copper) and PPT-11 (100 metres at 0.4 g/t gold including 4 metres at 1.69 g/t gold and 2 metres at 1.96 g/t gold).
Follow-up drilling consisted of six inclined RC holes 200 metres each in length and two diamond drill holes, TD-04 and TD-45. The holes intersected propylitically altered diorite, monzodiorite and andesite with minor calc-silicate horizons. Narrow zones of gold-copper mineralisation in the range 0.1-0.25 ppm gold and 0.1-0.25% copper were intersected in several of the holes.
SUMMARY
While a significant amount of historical exploration has been carried out on the tenement, very little effective, deep drilling has been done into the principal targets. Calibre believes that there remains significant potential to discover one or more Northparkes-style high grade porphyry copper-gold deposits on the property. A number of targets are drill-ready following minimal amounts of field work.
Calibre's approach to exploring Trundle will entail a thorough compilation and evaluation of the historical information including re-logging of the old drill holes. This work will be carried out in conjunction with field assessment of the main targets utilizing deep penetrating geochemical methods to refine the targets. Finally, a drilling program will be designed to test one or two of the highest priority targets in Q3, 2008.