One of the long-term aims of the Rosevale Mine project has been to clear the Deep Adit Level to its end, however, at present the full extent of the time and effort that will be required to achieve this is unknown. Once we had finished reopening access into the Deep Adit Level from the shaft on the hillside it was clear that it would be neither practical nor safe to attempt to clear a blockage that was known to retain a 10 metre head of water by working from the shaft. If we were to stand any chance of clearing the blockage that lay 150 metres from the shaft we would have to create a new access point closer to the blockage. This led us to decide to drill and blast a new 20 metre long tunnel and sink a 7 metre deep winze which would access the Deep Adit Level directly above the blockage. This was to be the biggest and most ambitious part of the mine project to date and it took a total of 12 years to complete.
Driving a new crosscut and sinking a winze to connect with Deep Adit Level
Schematic of the objective of the new crosscut and winze.
Driving the crosscut (1997 - 2005)
Work commenced in 1997. Although we had an Eimco 12B rocker shovel, we only had a small second-hand 100 cfm compressor, which was sufficient for working one Holman 303 rock drill, but did not have the capacity to work the rocker shovel. Therefore, we would have to hand muck into wagons after each blast, so we decided to keep the size of the tunnel as small as practical: 4 feet wide by 6 1/2 feet high. As we were not permitted to store explosives at the mine, generally we would drill the round at the weekend and then acquire precisely the right amount of powder to charge-up and blast during the week.
Starting the tunnel part way along No.2 Level proved not to be easy, but after a few blasts we were successfully on course. We expected that as the new tunnel got further from the lode, the granite would become harder and more competent, thereby lending itself to the use of high explosives. We hoped to advance 5 feet with each round. Unfortunately, the main problem that we encountered was that the rock became progressively softer and more weathered as we progressed away from the lode. This proved to be a real issue. Although the rock drilled easily, the blasts, especially the cut, often resulted in 'freezing' and we struggled to make good advance.
To ensure that we blasted each round as efficiently as possible, we drilled and blasted the cut and easers first and then drilled and blasted the outer holes and lifters. This made progress very slow. By the time we had almost finished the tunnel we had found that the best method was to wedge-cut the bottom half of the tunnel first and then blast the top half with horizontal holes. Also, in retrospect, it would have been better if we had used black powder in this soft rock.
Drilling the cut and easers
A typical blasting pattern Drilling with a Holman 303 rock drill The muck pile after a blast
After each blast the broken rock had to be mucked out into 1 ton wagons and trammed outside to be tipped and later to be recovered for re-use on site as hardcore. In general, it would take us two or three weekends to muck out after each blast. At regular intervals, as the tunnel progressed, new sections of rail track had to be laid. Eventually, by the end of 2004 (7 years later), the tunnel had reached a length of 20 metres - the point at which the winze would need to be sunk. We estimate a total of over 150 tons of rock had been removed.
Hand mucking Tipping Laying track
Work could now begin on sinking the winze to connect with Deep Adit Level.
Sinking the winze (2006 - 2010)
Another problem that arose was surveying. Although we had an accurate survey of the main workings, we could not get a line of sight down the access shaft into the Deep Adit Level. Therefore we were unable to accurately survey the adit and pin-point the position of the blockage. Three compass and tape surveys were run, but the naturally high level of iron oxide in the rock meant that the surveys were 3 metres different at the blockage. However, for the new winze to intersect the adit we needed to know its precise location. Our only choice was to take a gamble and commence the winze at the mid-point of the three surveys.
Sinking the winze was hard work. In order to minimise the amount of rock we had to remove we kept the size of the winze to 4 feet by 4 feet, but this was a tight space to work in. Also, as we progressed deeper, the bottom of the winze would flood between drilling the holes and charging-up which meant that the holes in the soft granite would collapse. To overcome this we had to use alkythene tube to line the holes once drilled. Initially the broken rock was hand hoisted out by bucket and rope, but this became inefficient as the winze was deepened, so an air winch was installed and an aluminium beer barrel was converted for use as a kibble. A concrete block wall was constructed around the chamber at the top of the winze to stabilise the ground and to provide a strong support for hoisting.
Eventually, the winze reached a depth of 7 metres, but there was no evidence of the Deep Adit Level, although the sound of the drilling could be easily heard through the rock in the Deep Adit Level. The winze was deepened to a depth of 9 metres, but still no sign of the adit. It was decided to drill pilot holes away from the bottom of the winze. On drilling the first pilot hole about 2 feet there water suddenly burst into the hole and quickly flooded the bottom of the winze. After 12 years we had at last hit Deep Adit. However, we had intersected the adit upstream of the blockage, so the next few weeks were spent working in water to enlarge the breakthrough into the adit level and set-up a permanent pumping system.
Top left: End of crosscut / top of winze: Top centre: Hoisting by bucket; Top right: Mechanised hoisting;
Bottom left: Charging-up in the winze; Bottom centre: Digging out the winze; Bottom right: Winze holed into flooded adit.
Completing the crosscut and the winze (2010)
Once the winze had been fully connected to the Deep Adit Level, the crosscut and winze had to be completed and equipped in preparation for clearing the downstream blockage in the adit. A short section of the crosscut passed through particularly poor ground and so sets of timber 'cap and legs' were installed to prevent spallation of the roof. Ventilation ducting was installed to provide fresh air down to the Deep Adit Level.
The start of the crosscut Timber 'cap and legs' in poor ground Finished crosscut
Extension to the waste tip point
The new winze completed
Our special thanks throughout this work must go to Gus Williams and the Camborne School of Mines, Peter Sheppard, Martin Orchard, Mark Kaczmarek and Mike Osman for all their help and advice throughout this part of the project.