Regional Geology

The oldest rocks are the Late Proterozoic to Early Cambrian Cape River Beds, which consist of schist, gneiss and quartzite, and crop out in the southern part of the Project area. Strongly deformed granites of probable Proterozoic age are exposed adjacent to the Cape River Beds (Figure 2). Both of these units were intruded by the Lolworth Batholith in the Late Silurian to Early Devonian.

Figure 2: Pentland Project Geology

There are three major centres of historical mining activity and several scattered smaller mining areas in the area of interest. The major centres are the Upper Cape Group Diggings, Mount Stewart Group and Lolworth Diggings (Figure 2). The Upper Cape Group Diggings are located near the southern edge of the Lolworth Batholith. Gold is found mainly in Tertiary deep leads within palaeochannels of the present Cape River. In the northern part of the Batholith gold-silver-copper mineralisation at the Lolworth Diggings and Mount Stewart Group is thought to be related to Permian and Carboniferous intrusions, including the Mundic Igneous Complex.

Figure 3 illustrates the location of prospects and known deposits in the district including the Thalanga copper-zinc massive sulphide deposit 25 kilometres to the south-east.

Figure 3: Pentland District Prospect Locations

Project Geology

The Toomba Prospect of the Pentland Project was identified from reconnaissance mapping, sampling and data collation of previously collected samples. It comprises a series of four NNE trending vein structures over an area of 1km by 1km. Three groups of old workings are reported in the area: Toomba, Toomba East and Lady Barrington. A further structure has been identified between Toomba and Toomba East, denominated Central. The main mineralisation takes the form of coarse-grained banded quartz - sulphide veins with abundant iron oxides hosted within a sericite altered granite.

The Toomba Prospect is situated in the east of EPM 12900 in the Pentland Project. The prospect consists of a semicircular area of gently to moderately undulating open ground with moderate outcrop, surrounded by an area of rugged hills with a high degree of outcrop.

It is not clear if the Amarra is a later intrusion within the Grasstree granite or if it is just an aspect of a partially exposed curviplanar contact. Locally the contact appears to be at a low angle with the Grasstree appearing to overlie the Amarra on some of the hilltops around Toomba. In general the low-lying ground of the Toomba prospect corresponds to the Amarra Granite and the hills around it are the Grasstree.

Recent and ongoing CYU exploration in Pentland:

  • Ongoing reconnaissance mapping along with rock chip and mullock sampling across the prospect. 6km of 100m Dipole-dipole IP survey has been completed over the Toomba prospect (figure 6). 6km of 100m Dipole-dipole IP survey has been completed over the Ralphs Ridge prospect.
  • 34.25 line-km of 25 x 400m soil-sampling has been completed over the Gap prospect.
  • 10.5 line-km of 25 x 250m soil-sampling has been completed over the Toomba prospect.
  • 30 line-km of 25 x 200m spacing infill and extension soil sampling program is underway over selected areas of the Gap prospect with the intention of refining the detail of the Au anomalies recently identified in this area and extending those that occur on or close to the limits of the existing grid.
  • 16 holes totalling 1887m of RC drilling in the Toomba prospect.

CYU undertook a thorough review of all available data from previous workers including analysis of aeromagnetic and radiometric data over several targets related to intrusions of the Permo-Carboniferous sub-volcanic Mundic Igneous Complex, which were considered highly prospective due to their similar age and style to units found in Mt Leyshon, Kidston and Ravenswood. This resulted in a focused plan of fieldwork targeting certain prospects, including Toomba, the Gap and Ralphs Ridge.

Of these, Toomba and the Gap are both considered to have many features that correlate to the proposed models of Mt Leyshon, Kidston or Ravenswood-style mineralisation. The Toomba prospect in particular has extensive historic workings and traces of mineralisation over an area of >1km. This prospect was focused on in order to develop drill targets and was successfully drilled during November 2008. Results from this primary phase of drilling are pending at this time.

CYU Completed Prospect-scale Exploration - Toomba

IP-Geophysics
The recent IP geophysical survey generated three distinct classes of anomalies over Toomba (figure 6).

  1. A group of NW trending planar anomalies appear to correspond to the regional tectonic fabric, as seen clearly in aeromagnetic surveys.
  2. Weaker, high-angle, planar anomalies are coincident with the known vein structures, especially the Toomba workings.
  3. A group of broad anomalies occur at depth in the SW and nearer surface in the east. These may represent larger, disseminated or breccia-hosted mineralisation at depth.

These broader deep targets are considered to correspond well to the model of an underlying blind intrusive breccia or disseminated stockwork style of mineralisation similar to that in Mt Leyshon or Ravenswood.

The group of broad shallower anomalies in the east of the survey correspond to areas of extensive float of veinlets in sericite alteredwallrock on surface with anomalous Au-values and coincident soil anomalies. These occurrences prove that there is potential for veinlet and stockwork formation in this area and that the granite is a viable hostrock for this style of mineralisation.



Figure 6: Toomba: 3D view from SSE of 2D IP Sections (with 10m Topo contours & IP anomaly trends).

CYU Soil Sampling

Soil sampling to mesh less than 80 micron was recently run over seven lines of 1.5km length at 250m interline spacing and a 25m sample interval. This included the four lines of the IP survey plus two further lines to the north and one to the south (figure 7).

The results produced several cohesive anomalies. Some of these correspond to the known mineralisation on surface, which confirmed the reliability of the sampling technique in this area. Several correlated to the previously identified IP anomalies, strengthening their validity as potentially mineralised targets, and others correspond to strike extensions of known structures, such as extensions of the old workings and Central further to the south and Lady Barrington extending to the north. In addition, there are strong multi-element anomalies in the NW, W and SE that require following up.

CYU Drilling

Detailed mapping and surface sampling are currently underway over the Toomba prospect. Historic workings and exploration pits have been found along the extensions of the Old Toomba workings, Lady Barrington, Central and Toomba East structures north and south to the limits of the existing soils grid (figure 8). Results returned from these sites have generated 1-3g/t Au anomalies from most locations in float, mullock and rockchips.

Figure 8: Map showing identified vein systems at surfaceand recent drilling. Note the East-West separation from significant intercepts is 500 metres. Continuity in these structures is probably in a North-South orientation. Significant mineralisation has been returned from holes PC005 and PC014.

Table 1: Results from rock chip sampling over the Old Toomba Workings.

Note: Mine spoil was sampled as well as outcrop since most mineralisation in outcrop was extracted efficiently by hand at the time of mining. Thus most outcrop samples are of lower grade.

A CYU drill program recently drilled 1887m in 16 reverse circulation drill holes. Of these, 12 holes were short to moderate depth holes intended to test the extent, width and grade of the mesothermal-style sulphidic quartz veins seen on surface. Six of these holes targeted theOld Toomba Workings(OTW) structure (one collapsed and was abandoned prior to its planned intersection), two tested the southern extent of the Central structure and three tested the Toomba East vein trend. Most of these holes made visible intersection of quartz and sulphidic-quartz structures. Since the analysis are still pending, it is not possible to expand on the results of these.

One hole tested the area of subcroping veinlets or stockwork with coincident IP and soil anomalies close to Toomba East. It is hard to distinguish the veinlets from the milky pegmatitic quartz in this hole, therefore opinion is reserved pending the geochemical results.

Table 2: Phase 1 Reverse Circulation drillhole details.

Non-alluvial historical gold production from the area has mainly come from narrow high-grade quartz lodes,like those at Toomba, and small structurally controlled intrusive breccia bodies such as the Lolworth Diggings. This type of mineralisation is of interest, but CYU's main target is intrusive related gold associated with Carboniferous to Permian subvolcanicintrusives. Similar age rocks host the Mount Leyshon (48Mt at 1.3g/t Au) and Kidston (80Mt at 1.3g/t Au) gold mines.

Subvolcanic intrusive breccias have been recognised at the Lolworth Diggings, Ralph's Ridge and Dead Horse Breccia.Recent soil geochemistry across the Gap prospect has revealed multiple strong linear gold anomalies trending 015o with lengths of up to 2.5km. Preliminary follow-up on these anomalies has shown them to be related to minor occurrences of veins and veinlets hosted in trends of sericite altered granite and very closely spatially related to parallel trending rhyolitic dykes similar to those of the Mundic Igneous Complex. Similar vein occurrences were also observed in shorter 300 trends, which may indicate a conjugate set of structures under a tensional strain regime.

The exploration model is based on an intrusive breccia-hosted or stockwork related target, related to Permo-Carboniferous shallow plutonic or sub-volcanic intrusives, such as the Mundic Igneous Complex, which is seen throughout the Pentland district.

Occurrences of these styles of mineralisation usually have certain features including:

  • Presence of Palaeozoic Intrusions, principally the Ravenswood-Lolworth Batholith.
  • Presence of Permo-Carboniferous intrusions, either subvolcanic or granitoids
  • Contacts of multiple lithologies, both intrusive and structurally controlled.
  • Strong structural features, often with co-genetic strain fabrics, such as en-echelon vein sets.

The following features are seen in or around the Toomba prospect:

  • The prospect occurs on a complex curvi-planar contact between the Amarra Granite and the surrounding Grasstree Leucogranite.
  • The Amarra Granite is apparently intruded by dykes and other minor bodies of the leucograniteand its associated pegmatitic phase. An amphibole-biotite-phyricgranitoid , seen in RC chips, appears similar to the Goldsborough Granodiorite phase of the Hogdon Suite. - These are all phases of the Lolworth Batholith locally, but indicate a complex and multiphase intrusive history.
  • It is possible that the narrow intersections of leucogranite bodies seen in the recent drilling actually correlate to similar phases of the Permo-Carboniferous Mundic Complex.
  • The Toomba prospect appears to lie on the intersection of a NW structure and a district-scale NE lineation seen as a linear limit to outcrop extending SW from Toomba. The Amarra Granite has been observed in outcrop trending NE up the Toomba/Barrington valley. It is possible that this is the line of a ridge or topographic high of the Amarra suite.
  • The strong NW linear IP anomaly is seen as a change in mineralisation style on surface and is parallel to the regional tectonic fabric, as shown in the district scale aeromagnetic images.
  • Most known hard-rock mineralisation in the district is aligned in trends along this NW orientation, with weaker NE conjugate sets.
  • The vein mineralisation is clearly observed to have sigmoid en-echelon form in outcrop, implying a dextral strike-slip component to the displacement at the time of formation.
  • The sub-volcanic dykes in the Gap mostly trend 015o or 300, paralleling the mineralised trends as seen in the soil-anomalies.

Table 3: Proposed Holes.

Figure 9: IP Sections showing proposed and previous drilling on sections 2850N & 3100N.

The Toomba prospect has a prospective lithological and structural framework that can be compared to Ravenswood and Mt Leyshon. It occurson the contact of different geological units with a potential deep-seated structural control, the presence of the distinct intrusive phases andpermo-carboniferous sub-volcanic units observed in the district. The historic workings and areas of subcroping veinlets prove that there is metal in the system. The IP anomalies have the characteristics of the target type postulated.

This is the first time that a company has explored for potential bulk-tonnage breccia or stockwork targets in this district. All previous work has focused on the potentially high-grade, butlimited volume, vein targets seen on surface. The geology and observed mineralisation style are considered compatible and comparable with other known occurrences of these deposit styles.

A proposed drilling programme has the potential to locate large tonnage gold mineralization and demonstrate that the Pentland Thalanga district is host to major economic gold deposits. The discovery of this style of large-tonnage, bulk-minable deposits would rejuvenate exploration activity in this part of north Queensland, which has fallen out of favour with many major exploration companies due to the current perception of small to medium tonnage of potential targets.