FIELD GEOLOGY OF THE SHOALHAVEN DISTRICT (PART 16)
Chapter 9 continued.
Excursion 9b
Ettrema Creek lies 1,200 feet below this fine vantage point and it is less than a mile to the opposite cliff. Downstream, the gorge becomes even narrower and deeper. Its very existence demonstrates that the uplift of this country occurred in comparatively recent times – otherwise the valley would have widened considerably.
Great cliffs of limestone occur along the creek 3 miles further downstream. These beds are probably of Silurian age, like the Bungonia and Marulan limestones and appear to be separated from the surrounding Devonian strata by a north trending fault. This appears on aerial photographs as a great gash, which seems to have faulted the Permian strata as well. The Ettrema fault is parallel to that previously mentioned at Touga and another at South Marulan.
Like many similar ventures, this mine failed because of its difficult access and the complexity of its ore. The brick chimneys and roasting ovens by the river are evidence of an attempt to mine the ore about 60 years ago. Across the river, the scar left by an old flying fox cable is still plain today.
Alluvial gold may be washed from the river gravel, especially when the water level is low.Touga, Tolwong, and the Ettrema Gorge (70 miles return)
The spectacular scenery of this country has been explained earlier. Most of the features of geological interest are to be found in the older rocks, beneath the Permian cover. This is the most mineralised area in the Shoalhaven district and one suspects that great mineral wealth lies undetected beneath hundreds of feet of Permian sandstone.
Route: Sassafras-Touga-Quiera-Tolwong
Leave the Braidwood road about 5 miles past Sassafras and 1.3 miles before the descent to the Endrick River.
The road passes over sandstone of the Berry Formation for about 3 miles and then over the Nowra Sandstone at a place locally called ‘The Jumps’. The narrow ridge along which the road passes is besieged on both sides by deep valleys, which at this point have eaten away a large part of the sandstone. This road is part of a route used by bullock teams and drovers in earlier days, taking a rather direct route to Sydney.
Turn left for Touga 2 miles further on. The right branch leads to Tolwong. It is nearly six miles from here to the homestead and as most of this is in private property, visitors should ask permission from the landowner before leaving the road. Places of geological interest will be treated in their order from the Tolwong road.
The road passes over extensive areas of bare rock just before outcrops of slate are reached, 3.4 miles from the fork.
Stop 1. There is a marked unconformity between the Shoalhaven Group sediments and the underlying Ordovician metamorphic rocks. From graptolites found in the locality, these rocks are known to be of Upper Ordovician age.
Continue towards Touga. Stop at the second gate after Stop 1.
Stop 2. A view of the Shoalhaven gorge may be had in this vicinity. Copper was discovered nearby in the late nineteenth century. The site of the old diggings is about ½ mile east of the road, just below the junction of Touga and Quiera Creeks. This is the only major creek junction in the area and lies about 350 feet below the road.
Copper stained slate marks the outcrop of several bodies of quartzose chalcopyritic ore. The largest of these is a vein 2 ½ feet thick and it proved to be patchy and uneconomical to mine.
Alluvial gold occurs in Touga Creek down to its junction with the Shoalhaven. This is about 5 miles downstream and a considerable amount of prospecting has been carried out towards the junction.
Continue towards Touga. Outcrops of a granitic rock may be seen on the left.
Stop 3. Instead of the expected granite, the rock proves to be a variety of gabbro called norite. It consists largely of pyroxenes and plagioclase with smaller amounts of olivine. Creeks draining this intrusion also carry alluvial gold. After so many miles of barren sandstone country, it is quite a change to reach this open country, with its views of the Shoalhaven River and the hilly country beyond.
Touga homestead is about 1 mile past the first norite outcrop.
Stop 4. There is much to be seen by walking due west towards the gorge. The river follows a fault, separating Touga from a similar igneous body across the valley. From the homestead to the river is a drop of over 1,200 feet, mostly by precipitous slopes. Immediately opposite is the impressive canyon of Nerrimunga Creek, which has cut a great gash in the side of the Shoalhaven gorge.
Return to the Tolwong road, turn left and stop 1 mile further on where the road crosses an extensive area of bare rock.
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| Ettrema Gorge November 1967 |
Stop 5. This is the nearest any road approaches to the Ettrema gorge, which can be seen less than a mile to the east. The return walk to the cliff edge takes about an hour. Keep to the right of the small valley to avoid dense undergrowth. The sandstone ridge is thick with many varieties of wildflowers, which add interest to the walk.
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| Ettrema Gorge November 1967 |
There is a great deal to be learned by descending into the gorge (allow 4 hours return) but this is not an easy climb nor are the most interesting features immediately below this point. The cliff may be avoided by walking southwards until a gap is found, where a small stream has carved a notch. Even so, some scrambling must be done. Only the Nowra Sandstone is present here, resting on the same kind of Ordovician slate seen at Touga. On the opposite side of the gorge, however, it appears that older members of the Shoalhaven Group lie beneath the sandstone. The slate soon gives way to quartzite and reddish siltstone of probable Upper Devonian age similar to the rocks seen at Yalwal and east of Nerriga. These persist all the way to the bottom, where a surprisingly small stream trickles over a rubble choked bed. There are dangerous scree slopes to be avoided on the descent. If these were to be set in motion any climber in the vicinity would be in an awkward position.
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| Ettrema Gorge November 1967 From the bottom looking up. |
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| Ettrema Gorge November 1967 The creek at the bottom. |
The limestone is known to contain caves, but little is know about them. There has been extensive mineralisation in the limestone and the old Ettrema Mine was opened up here many years ago. A complex sulfide ore body outcrops in Jones’ (or Rolfe’s) Creek, about 1 mile above its junction with Ettrema Creek. It occurs as a replacement deposit in the limestone and its principal minerals are sphalerite, arsenopyrite, galena, and chalcopyrite. Tin and silver are also present. Some ore was mined, but because of the difficulty in removing it from the gorge, most of it remains there to this day.
Continue towards Tolwong. About 1 ½ miles further on, the road passes onto an outlier of basalt.
Stop 6. The Quiera basalt, at an elevation of 2,400 feet, strongly resembles that seen at Sassafras and Tolwong. These all appear to be remnants of a former sheet which extended south from the Moss Vale district before the uplift.
The cleared ground, with its rich soil, is a pleasant change from the miles of poor country around it.
About 4 miles past Quiera, the track descends to a small outcrop of basement rocks near Tullyangela Creek.
Stop 7. The total thickness of the Shoalhaven Group seldom exceeds 300 feet in this area, which evidently lay near the edge of the Permian sea. Erosion has exposed granite and slate, similar to that seen near Touga. The peculiar course of Tullyangela Creek may be due to recent stream capture or the re-excavation of an old valley buried under the Permian sediments.
Tolwong homestead lies about 7 miles further on, where there are extensive areas of basalt country. Enquiries should be made here before proceeding further.
Stop 8. The basalt extends almost to the edge of the gorge, about 500 yards north of the homestead. Tallowal Creek has cut a steep valley which descends 1,800 feet to the Shoalhaven River. The track continues on for 3 more miles to a point above Badgery’s Crossing, which was an important stock crossing in the early days of settlement.
The Tolwong mines are reached by turning left just before Tolwong itself. The track is poorly defined and crosses fairly level, timbered country for 4 or 5 miles until the edge of the Berry Formation is reached. A well defined foot track then descends to the river, passing the various mines in a gradual 1,500 feet descent.
Stop 9. The main ore body resembles the Ettrema lode in its mineral composition. It is first met with as an outcrop of green copper-stained slate about half way down. From this point on, the lode varies in width from a few inches to over 8 feet. It appears to have been deposited as a vein within Ordovician slates by an unexposed igneous body and is one of the best documented lodes of its type in NSW. The main ore mineral is arsenopyrite, with lesser amounts of galena, sphalerite, chalcopyrite, and stannite. Quartz and fluorite are prominent gangue minerals.
Specimens of all of these may be had from the various mine adits and natural outcrops or from mullock heaps near the river.
The old workings are unsafe and should not be entered, nor should the creek water be drunk because of its arsenic content.
In several places, water flowing from abandoned tunnels is richly coloured by copper.
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| Tolwong mines December 1974 |
This is difficult country for the prospector, but mineral wealth may yet be extracted here. It is about 3 miles from here to Bungonia Caves, and 7 to Long Point Lookout at Tallong. Both walks are rather strenuous and involve crossing the river, but cover some very scenic country.
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| The Blockup, Shoalhaven River. December 1974 |
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