DRILL SPEED AND DRILL TYPES
How many holes can an NQ-drill do per day and how many meters per day can three rigs manage? These are questions I regularly get from readers impatient with the pace the company in question drills at.
There are a few types of drills used for exploration drilling and all of them require an rotary drill and a metal tube with an core bit in the front made of diamond. The drill bit is lowered down to the surface and rotated against the rock surface. A friction is accomplished and water is used to get the rock dust to the surface so that the drill bit can work freely again. The rotary drill needs a lot of power and the bigger core you need to get, the more power you will need to accomplish. Bigger cores often means shallower drill depths also. Some 300 meters is often mentioned as normal in exploration drilling.
There are 8 often tube sizes used, where AQ-drilling is the smallest with only 48 mm of outside hole diameters and 27 mm core diameter. This drill type is used for very deep or fast drilling where structure is searched. BQ is the next tube size with 60/36,5 mm is accomplished. This drill tube size is not very common. NQ-drilling is very common with 75,8/47,6 mm is achieved. This tube size is something in the middle, both fast and gives a great amount of material to the surface. GBB used this tube size for phase 1 and 2. There is also HQ and PQ tube sizes which are 96/63,5 and 122,6/85 mm in diameter which requires a lot of power from the drill rig at the surface. A larger core diameter means that the analyzes can be more accurate because of the larger core sample and the “nugget effect” is lower.
Core used for:
When the drilling has finished at the hole, the core is split in two pieces, one is sent to the analyzing labs and one piece is placed in a rack, with number that tells what hole it comes from and what depth. Often the geologist at site mark points of interest on the drill core and photograph the core for further analyzing in the office.
A normal drill speed for NQ drilling is around 5-10 meters per hour without stop. The drill speed depends on numerous factors, for example rock type, homogeneous rock, wear of the drill bit, flow of water, depth of drilling, terrain and more. An example of drilling in one 24-hour period: 7,5 meters x 24 hours = 187,5 meter/day. To drill 2500 meters you will need the following numbers of days before finishing: 2500 meters/187,5 meters = 13,5 days with no stops for maintenance.