The article discusses reasons for using room and pillar mining methods to mine the Saskatchewan’s Potash Deposit.
Introduction
Room and pillar mining method technique is most suitable for flat-lying deposits, such as those that follow a particular stratum. This is a naturally supported mining method, in which the ore is left behind as pillars to support the back of the mine. Conventionally, once the mining of the orebody is completed, pillar extraction is performed to mine the remaining trapped ore in the pillars. This step is not performed in the room-and-pillar mines designed to mine potash.
Room and Pillar in Potash Mines
Potash deposits are overlain by a number of water bearing formations. These water zones are also found in the footwall of the ore deposit. Potential inflow of water can dissolve the salts found around the potash deposits. In this way, this will result in unstable ground conditions, which may result in collapse of the roof. Inflow of water creates hazardous situations for the miners and in serious issues it can even result in closure of the mines.
Longwall mining is usually used to mine long horizontal deposits like potash. However, longwall mining results in subsidence of the ground. The potash deposits are overlain by water bearing startas, any ground subsidence will result in inflow of the groundwater in the mine. This can be very catastrophic as this will dissolve the salts found around the potash deposits. To prevent this happening, the pillars are left behind in the ore body for the roof support to mitigate any possibility of the roof collapse.
Saskatchewan Potash Development:
Nearly 400 million years ago a vast sea covered most of Saskatchewan. Over time, a massive reef slowly grew across the northern part of the Saskatchewan. This reef cut off the connection with the main ocean and more ocean water could not seep inland. The warm and dry air climate eventually evaporated the water that was trapped inland, this produced a bed of mineral salts, today known as the Prairie Evaporite Formation. This formation contains the world’s largest known reserve of. The province of Saskatchewan alone accounts for almost half of the world’s potash reserves. Potash deposits in Saskatchewan are located about 1,000-3,000 meters below the earth’s surface and are relatively flat-lying and undisturbed over very large areas. Potash ore is composed of approximately 55 percent sodium chloride, 40 percent potassium chloride and 5 percent clay and other insolubles. It also contains small amounts of iron oxide which gives the finished product pink or red color.
Potash ore is extracted from two major ore deposit types, deeply buried marine evaporite deposits that typically range from 400 metres to greater than 1,000 metres below the surface, and surface brine deposits associated with saline water bodies such as the Dead Sea in the Middle East and the Great Salt Lake in North America.
All commercial potash deposits are originated from marine deposits buried deep in the earth. Potash ores are typically rich in potassium chloride (KCl) and sodium chloride (NaCl).
Most of the world reserves of potassium were deposited as sea water in ancient inland oceans. After the water evaporated, the potassium salts crystallized into beds of potash ore. The deposits are a naturally occurring mixture of potassium chloride (KCl) and sodium chloride (NaCl), commonly known as table salt. Over time, as the surface of the earth changed, these deposits were covered by thousands of feet of other minerals and soil due to the weathering of rocks.
Hydrogeology in Potash Mines
Hydrogeological mapping plays a vital role in case of potash mines for two major reasons. First, to identify the sources of water supply for mining and processing operations and second is to identify the risks involved with the groundwater inflows at the shaft and slope sites. Contamination of aquifers and water table lowering are also concerns in potash mining.