GEOLOGY

The Tooloom goldfield lies within the Emu Creek Block, a tectonic unit within the New England Fold Belt of north eastern NSW. Rocks in the area consist mainly of gently folded conglomerate, sandstone, siltstone, carbonaceous siltstone and tuff of the Emu Creek Formation, thought to be of Permo-Carboniferous age. Regionally these sedimentary rocks are intruded in a number of places by granitic to dioritic igneous rocks of Permian to Triassic age. This setting and age relationship are quite similar to those of gold mineralisation at Gympie, some 260 km to the north in Queensland. Within the Tooloom project area mapping by Malachite has identified several previously unrecorded bodies of intrusive rocks, including felsic porphyry, quartz diorite porphyry, hornblende diorite porphyry, diorite, microdiorite and dolerite. Hydrothermal alteration and sulphide mineralisation are well developed in many of the intrusives and in their sedimentary wall rocks.

To the east and north, the Emu Creek Formation and the intrusive rocks are overlain unconformably by Jurassic-aged coal measure sediments of the Clarence – Moreton Basin and they in turn are overlain locally by Tertiary basalt lava flows. Perched fossil alluvial deposits (“deep leads”) occur on some of the ridges beneath and projecting out from under the Tertiary basalt. Some of the deep leads have been worked for gold. The region displays a strong structural grain, clearly visible in the aeromagnetic image, with dominant NNE and NW structures which affect drainage and commonly control mineralisation. Dilation zones occur in many places and some contain intrusions of porphyry, bodies of hydrothermal breccia or sheeted auriferous quartz veining. Mineralisation at Tooloom is clearly associated with intrusive centres, with a variety of expressions in different host rocks and structural settings. Overall a strong analogy between gold mineralisation at Tooloom and that of the Tintina belt in Alaska and the Yukon is recognised. This style of gold mineralisation is commonly described as intrusion related or reduced-intrusive related gold.

GEOPHYSICS

In 2000 a helicopter-borne aeromagnetic survey was undertaken at Tooloom. The results clearly show a spatial relationship between most known prospects and magnetic highs (see image to the right). Furthermore, a strong north-northeast structural grain is evident in the magnetic data, consistent with observations on the ground that many faults and intrusive dykes are oriented in this direction. A lesser northwest grain is also apparent in the magnetic data and some prospects seem to favour this direction (e.g. Pine Gully).

The Phoenix prospect does not readily stand out at the scale of the image on the right, but when data for the Phoenix area are extracted and some filtering applied to the very strong high just to the north a very interesting, roughly circular feature is very evident in the magnetic data (see image in Phoenix page). This feature is approximately 2km across and seems to enclose the core area of brecciation and mineralisation as currently known at Phoenix.

In late 2006 a new helicopter-borne aeromagnetic survey was flown, covering the whole of EL 6263. New targets have emerged from that work and these will be the subject of follow up field work and, if appropriate, drilling in 2007. At the same time, selected parts of the area were also covered with an airborne electromagnetic survey.

GEOCHEMISTRY

By far the most powerful tool for identifying new hard rock gold occurrences at Tooloom has been stream sediment geochemistry, particularly using the Bulk Leach Extractable Gold (“BLEG”) technique. Experience has shown that values above 5 ppb Au are anomalous at Tooloom and most key prospect areas typically are expressed by anomalies of the order of 50-80 ppb Au. Interestingly, however, some gold occurrences give rise to much more weakly anomalous stream sediments. Back Creek, for example, has a BLEG anomaly of only 8 ppb Au, even though coarse grained, visible gold occurs in outcrop just upstream. Numerous stream anomalies of the order of 5-10 ppb Au are yet to be followed up in the broader Tooloom goldfield area and some could lead to discovery of new prospects like back Creek.

The map on the right summarises the results of stream sediment geochemistry conducted across the Tooloom area.

MINERALISATION & ALTERATION

Gold mineralisation at Tooloom is characteristically coarse grained. Nuggets are common and visible gold can be seen in outcrop at Back Creek. Panning of the more anomalous soil samples commonly reveals gold particles of the order of 1mm or so in size. Several different styles of mineralisation have been recognised, some hosted by dioritic intrusive rocks and others by sediments of the Emu Creek Formation. Even in the latter case, however, there seems to be a distinct affinity with nearby intrusive activity. Within the intrusives the gold may occur within stockwork quartz veins or in disseminated form, associated with suphides. Within the Emu Creek Formation gold may occur in linear structures, either within anastomosing quartz veins in low pressure dilational zones or in sub-parallel sheeted quartz vein sets. In some places there are stockwork quartz veins within Emu Creek Formation sediments, particularly the more brittle sandstone and conglomerate members (e.g. Back Creek and Joes Gully). The Emu Creek sequence includes some carbonaceous beds but so far the only place where gold has been found clearly associated with carbonaceous rocks is at Pine Gully.

Mineralised breccia is also present in a number of prospects, most notably at Phoenix, where the breccia appears to be hydrothermal and is a major host to gold mineralisation. Elsewhere, as at Pine Gully, the brecciation seems to be of tectonic origin. Some breccia bodies, such as that at Cullens, contain pyrite but virtually no base metal sulphides or gold.

Sulphide minerals are generally present with gold, most commonly arsenopyrite, pyrite and pyrrhotite. Minor chalcopyrite has been observed at Frasers and Phoenix, while stibnite is well developed at Phoenix.

In terms of alteration mineralogy the main secondary minerals observed are sericite and carbonate, commonly quite intensely developed. In some cases the sericite is relatively coarse grained and the host rock is reminiscent of greisen. Silica flooding is evident within some intrusive host rocks and in some sediment-hosted structures gold is accompanied by banded quartz, carbonate, sericite and chlorite alteration.

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