Some countries have specific definitions for resources and reserves. An attempt is made to make these consistent among countries for a mineral commodity. For example, the Australasian Joint Ore Reserves Committee (JORC) established the Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves (the JORC Code) that sets out minimum standards, recommendations, and guidelines for public reporting in Australasia of exploration results, mineral resources, and ore reserves. Companies listed on the Australian Securities Exchange and the New Zealand Stock Exchange are required to report publicly on ore reserves and mineral resources under their control, using the JORC Code (http://www.jorc.org/).
In Canada, the Canadian Institute of Mining, Metallurgy, and Petroleum (CIM) provide standards for the classification of mineral resources and mineral reserves estimates into various categories. The category to which a resource or reserve estimate is assigned depends on the level of confidence in the geologic information available on the mineral deposit, the quality and quantity of data available on the deposit, the level of detail of the technical and economic information that has been generated about the deposit, and the interpretation of the data and information. For more information on the CIM definition standards, see http://www.cim.org/ UserFiles/File/CIM_DEFINITON_STANDARDS_Nov_20 10.pdf.
Russian resources and reserves data are often published according to the Soviet reserves classification system, which is still in use in many countries of the former Soviet Union, but also at times published according to the JORC system based on analyses made by Western firms. It is sometimes not clear if the reserves are being reported in ore or mineral content. It is also in many cases not clear which definition of reserves is being used, as the system inherited from the former Soviet Union has a number of ways in which the term reserves are defined, and these definitions qualify the percentage of reserves that are included. For example, the Soviet reserves classification system, besides the categories A,B,C1, and C2, which represent progressively detailed knowledge of a mineral deposit based on exploration data, has other subcategories cross-imposed upon the system.
Sotkamo Silver applies SveMin’s & FinnMin’s respective rules of reporting for public mining & exploration companies. Sotkamo Silver has chosen to report mineral resources and ore reserves according to the internationally accepted JORC or NI 43-101-code. The company applies International Financial Reporting Standards (IFRS) as approved by the European Union.
Exploration geology can be done near existing mines or in areas where there is no evidence of previous mining, however, all work must be conducted within claims and mining leases.
Exploration geologists use many different types of data to determine where metals may be found. The datasets can be very large and complex and require computers to process the data and to display it in a form that can be analysed. A large array of sophisticated geological, geochemical and geophysical technology is available to geologists so that they may add to their understanding of the rocks below the surface.
Exploration may start with studying aerial photographs, published geological maps and reports written by previous geologists who have worked in the area. Ground or air geophysical surveys may be conducted to measure variations in the magnetic and electrical properties of the rocks or mineralisation below the surface.
By using computer-generated models, potential targets are found by determining areas that have a high probability of containing ore grade rocks. The area should at the same time have low confidence due to insufficient data (insufficient drill holes) i.e. the presence of ore has not been proved.
Once geologists have assessed and analysed all these data, a first pass drilling program may be done to determine the metal content below ground. Once an area of anomalous metal values has been outlined a reverse circulation (RC) drill rig is used to collect deeper samples at depths of up to 800m. A diamond drill rig can also be used and can drill to depths of 1000m or more. A diamond rig is expensive to operate but produces cylindrical cores that provide valuable information about the rock and metal mineralisation.
If mineralisation is located, additional drilling is undertaken until the shape and size of the orebody is known. A large amount of data must be compiled on the orebody before it can be mined. This work is then completed by Resource Definition geologists.
If drilling fails to locate sufficient mineralisation for mining, the area shall be rehabilitated back to how it was prior to the commencement of exploration activities. This involves the removal of drill hole collars, back-filling of holes and scarification of the drill site so that plants can regrow.
Data is obtained through drilling. Typically two types of drill rigs are used:
- Reverse Circulation (RC) percussion drills, and
- Diamond Drills
RC drills pulverise the rock and force the samples through the drill rods by using high-pressure air. Pulverised rock is retained in a dust collector where the sample is subdivided. The subdivided samples are then sent to a laboratory for metal and sulphur analysis. Another set of rock chips are tested by the Geologist for rock type, alteration, and structure.
The diamond core is also logged by the geologist. The core is cut in half (long ways) using a diamond saw. The half core is then bagged into composites and sent to the laboratory for analysis.
All this data is then used to generate a computer model of the metal content variation, rock types and structures that contain the different metals.
Once drilling in an area is completed the geological model is re-evaluated. The evaluation re-determines the grade, tonnes and confidence of the area. Estimations are made by using complex computer algorithms that search for drilling data within the generated model and estimate grades for ore blocks based on geological assumptions programmed into the algorithm.
Production Geologist is responsible for the grade and tonnage that is mined from the ore lodes each day. They must also ensure that all of the lodes are trucked from the pit floor up to the plant.
To find the ore lodes the Mine Geologist must plan the drilling and take samples of the rock beneath the pit floor. The holes are drilled for ex. every 10 metres along the lode and 8 metres across. Samples are collected every 1-2 metres down the drill hole. The samples are then sent to the laboratory for assaying.
When the metal grades are sent from the laboratory, the geologist must plot the position of each of the drillholes onto a plan. From the plan, a map is produced where the ore lodes occur. From the map, the tonnes and grade of the silver in the rock to be mined are determined. This map is used by the mine engineers, who drill and blast all rock with explosives so the rock can be broken and dug by the face shovels. The map is also used by the Mining Engineers so they can mine and truck the ore lodes to the mill and truck the waste rock to dumps that do not contain ore lodes.
The Mine Geologist must then work closely with the Drill and Blast Engineer to determine the best way to blast the rock in the ore.
The Surveyors survey the boundary's of the ore lodes by use of equipment that receives coordinates from satellites or underground markings.
The Mine Geologists work closely with the Mining Engineers so that all ore lodes are mined. It is the Mine Geologists task to determine the way the ore lodes are mined by the shovels. They often sit in the face shovels with the miners to ensure that only the ore lodes are mined, and that rock that does not contain any economic silver is trucked to a waste dump.
The Mine Geologist must also work with the Metallurgist to assist them in extracting the maximum amount of silver in the Mill Processing Plant. The Geologist informs the Metallurgist of the grade of the silver in the ore lodes and the amount of sulphur that occurs in them.
After the ore has been treated the Geologist compares the estimate of the ore that was mined with the metal that was recovered. This process is called reconciliation. The Geologist does this study to help to identify if there are any problems in the method of identifying and mining the ore.
Open pit mining requires close attention to geology, geotechnical planning, scheduling of earthmoving equipment, drill and blast technology and safety. Through constant monitoring and improvement, each aspect of open pit mining aims to control and reduce costs and improve the extraction of ore from the ground in the safest, most efficient manner.
A planned sequence of events is involved in mining a pit:
- identify the resource
- extract it
- transport the ore to be treated in a mill to produce a metal concentrate.
The sequence can be considered as a cycle of events, where each revolution of the cycle represents an increase of the pit depth by one bench (equivalent to 10 metres).
Designing the mining layout and blasts
Before any hole is drilled or rock mined, much planning goes to make sure that the mining sequence runs smoothly and as safe as possible. The mine planning engineers, in conjunction with geologists, drill and blast engineers and voids officers, design the size and shape of the blasts. These issues are taken into account:
- location of the ore on the bench
- presence and intensity of former work
- ore requirements of the mill.
Plans and schedules are checked by all relevant parties and, when agreed upon, mining begins.
Underground hard rock mining refers to various underground mining techniques which are used to excavate hard minerals. Mainly those minerals containing metals such as ore which contains gold, copper, zinc, nickel but also involves using the same techniques for excavating ores of gems, such as diamonds.
Accessing underground ore can be achieved via a decline, inclined vertical shaft.
- Declines can be a spiral tunnel which circles either the flank of the deposit or circles around the deposit. The decline begins with a box cut, which is the portal to the surface. Depending on the amount of overburden and quality of bedrock, a galvanized steel culvert may be required for safety purposes. They may also be started into the wall of an open cut mine.
- Shafts are vertical excavations sunk adjacent to an ore body. Shafts are sunk for ore bodies where haulage to the surface via truck is not financially efficient. Shaft haulage is more cost-effective than truck haulage at depth, and the mine may have both a decline and a ramp.
Declines are often started from the side of a high wall of an open cut mine. When the ore body is of a grade to support an underground mining operation, but the strip ratio has become too great to support an open cast extraction methods. They are also often built and maintained as emergency access from the underground workings and a means of moving large equipment to the workings.
Levels are excavated horizontally off the decline or shaft to access the ore body. Stopes are then excavated perpendicular (or near perpendicular) to the level into the ore.
Development mining is composed of excavation almost entirely in (non-valuable) waste rock in order to gain access to the orebody. Production mining is further broken down into two methods, long hole and short hole. Short hole mining is similar to development mining, except that it occurs in the ore. There are several different methods of long hole mining. Typically long hole mining requires two excavations within the ore at different elevations below the surface, usually between 15 - 30 metres apart. Holes are drilled between the two excavations and loaded with explosives. The holes are blasted and the ore is removed from the bottom excavation.
The treatment process
The treatment process involves many steps:
- 2. Grinding
- 3. Froth flotation
Crushing involves tipping ore into a crushing machine. Usually, trucks tip the ore directly into the crusher.
Grinding is the process that breaks fist size rocks to very fine particle sizes. This is done in large rotating mills that look like big steel drums. These mills are called SAG mills or ball mills. Inside these mills contain various amounts of small or large steel balls that are rotated to cause collisions with the rock fed to the mill. The balls break the rock fragments into extremely fine rock particles. Water is added to this process to ensure that all fine particles are flushed from the mill to the next process.
The size of rock particles after milling is less than 1/5 of one millimetre. To break rock to this very fine size involves the use of a lot of electrical power.
All rock particles formed during grinding now go with added water to the mills. This mixture is called a slurry. The slurry is transported around the treatment plant by special pumps.
This process uses chemicals to collect included metals into a concentrated form.
Chemicals are added to the slurry from grinding. These chemicals attach themselves to certain minerals in the slurry. All slurry is pumped to large tanks called flotation cells. Air is added to the bottom of flotation cells and rises through the slurry. The chemicals added are hydrophobic so they attach themselves to the passing air bubbles and float to the top of the cell. When the air bubbles reach the top of the cell they form a froth much like the top of a cappuccino. This froth contains nearly all silver. gold and other metals.
When the froth becomes too full it spills over the edge of the flotation cell and is collected into a launder. The launder contents are discharged and pumped into storage tanks.
Finally, the contents of these tanks are passed over a vacuum filter. The process water is reused in the process. The high-grade solids that are left are virtually dry, so they can be conveyed to a stockpile then loaded into trucks and sent to the roaster site for further treatment.
The material that did not float is called tailings. Tailings is the word used to describe slurry with very low silver and metal content.
The flotation tailings are passed sent to a large storage dam.