WHAT’S NEW Walking on water

Exploration companies are discovering they don’t have to wait until freeze-up to perform induced polarization (ip) surveys over lakes. This past summer, on the waters of Red Lake, Ont., the rubber boat Electric Ark tested a new geophysical exploration system that promises to revolutionize exploration for gold deposits beneath lakes of the Canadian Shield. Developed by Hardy bbt, a consulting engineering company in Calgary, Alta., the system produces ip data at a faster rate and at lower cost than winter surveys carried out on the ice. It is called a micro-processor- controlled, waterborne, induced polarization system–micro wip for short.

In tests the micro wip system produced up to 10 km of ip survey line data per day from the 20-ft boat.

Productivity from the ice in winter is considered good at 5 km of line per day. Costs range from $700 to $1,500 per line km. Not only has production increased significantly with the micro wip system, but the cost has come down to about $600 per km plus mobilization (usually about $6,000- $10,000 per lake), depending on location, says Brian Dowse, Hardy’s senior vice-president.

The micro wip system had its beginnings when Hardy bbt’s chief geophysicist, Dr William Scott, worked for the Geological Survey of Canada in the 1970s. In 1980 Scott joined Hardy bbt in Calgary, and over the next few years the system was perfected at considerable expense and effort. (Hardy bbt is a wholly-owned subsidiary of Saskatoon, Sask.-based Agra Industries, a diversified public company listed in Toronto and Montreal.)

The final field testing of the micro wip system was completed in 1985 and a grant from Energy, Mines and Resources last winter allowed Hardy to develop the software necessary to process geophysical data in real time on board the Electric Ark. This was a major breakthrough, Dowse says, because it allowed geologists to assess the data at the end of each day’s work. Adjustments can be made in the next day’s survey, if necessary, thereby avoiding the problem of exploring blind.

For a client, the mechanics of a micro wip survey are simple. Provide Scott with a map of the lake to be surveyed with survey lines marked. He will then pick out the locations for the navigation slave stations for the on-board navigational system. These stations (usually four per lake, all within 10 km of the lines) must be surveyed and the co-ordinates provided to Hardy before the crew arrives at the lake.

The Electric Ark arrives at the lake on a trailer (or by Twin Otter plane in the case of remote lakes). The slave stations are set up at the pre-surveyed locations around the lake. The rubber boat is put into the water, the slave co-ordinates are punched into the on-board micro-computer (an hp-9816) and the survey starts. The Electric Ark tows specially designed cable electrodes behind it at about the speed of 2 km per hour, and the results are printed out as pseudo-sections on the boat. At the end of each survey day, the client receives a hard copy printout of the results. These include ip, resistivity, magnetics and a sub- bottom profile.

Although up to 30 km of line have been surveyed in a 24-hr period, the average daily target is 8-10 km depending on the complexity of the lines. The boat driver steers by watching the line on the monitor mounted in front of him and he can correct his position when he is a few metres off line. The survey lines can be recovered in the field to within a couple of metres.

The micro wip system promises to revolutionize waterborne surveying for gold in Canada. It could also be used for detecting submarine deposits of gravel for island construction in the Beaufort Sea and for exploring offshore placer deposits. In 1985 it was used to delineate submarine permafrost zones in the Artic offshore.

Hardy has a busy exploration season lined up as many companies discover they don’t have to wait for winter to do their ip surveys.