Diamonds are the hardest natural substances. They are made up of single element carbon. A huge amount of feed and pressure under the earth's surface causes the carbon atom to bond in a unique way that results in the formation of a beautiful and crystalline structure the diamond.
Types of Mining:
There are two types of pipe mining.
1. Open-pit Mining
2. Underground Mining
1. Open-pit Mining:
Open-pit mining involves removing the layers of sand and rock found just above the kimberlite. Once exposed, the ore in the pit is broken up by blasting. A single blast can break approx. 3,000 tonnes of ore. Once the ore is broken, excavators load the ore into haul trucks and transport it to a primary ore crusher where the diamond extracting process begins. The Kimberley Big Hole is an example of open-pit mining.
2. Underground Mining:
In underground mining, miners tunnel through Earth’s crust to the kimberlite pipe. Tunnels are constructed in two levels, one above the other with funnels built to connect the two. Mining begins on the top level by blasting ore, which falls through the funnels and collects on the second tunnel. Here, loaders collect the broken ore and bring it back to the surface for processing.
Over thousands of years, the kimberlite pipe that reaches the Earth’s surface is eroded and weathered by wind, rain, rivers, and streams. The eroded kimberlite bears rough diamonds, which are carried downstream. The first diamonds discovered in South Africa were from alluvial deposits.
Today, industrial alluvial mining involves building a large wall to collect the water in one area. Diamonds are often found in the gravel layer, which collects under layers of other material, such as mud, clay, and underwater plant life. Once the gravel is collected, it is hauled to the surface and prepared for processing.
Marine Mining:
Marine mining involves extracting diamonds from the seabed, hundreds of meters underwater. The earliest form of marine mining entailed shore diving, where a swimmer would collect diamond-bearing gravel from the shallow seabed. Today technology has evolved to specialized ships that mine for diamonds deep out at sea.
Diamonds are recovered from ore in 5 stages:
Stage 1 – Crushing:
Once the diamond-bearing ore and gravel are collected, it is transported to a primary crusher. The primary crusher is responsible for reducing the size of the ore into smaller, more manageable pieces or chucks measuring no larger than 150mm. A secondary crusher, known as a roll-crusher, may also be used to reduce the size of the ore even further.
Stage 2 – Scrubbing:
In this stage, the ore is scrubbed to remove loose excess material and is screened. Material smaller than 1.5mm is discarded because it is too costly to extract diamonds from such a small piece of ore.
Stage 3 – Cyclonic separation plant:
During this stage, the diamond-bearing ore is mixed with a solution of ferrosilicon powder and water, which is measured to a specific relative density. This solution is fed into a cyclone, which tumbles the material and forces a separation. Materials with a high-density sink to the bottom result in a layer of diamond-rich concentrate.
Stage 4 – Recovery:
Here, the diamond-rich concentrate is put through a series of processes involving magnetic susceptibility, X-ray luminescence, and crystallographic laser fluorescence that are calculated based on the specific properties of diamonds. These processes are designed to separate the rough diamond from any other heavy-density materials collected by the cyclonic separation plant. For example, a diamond’s fluorescence when exposed to an X-ray. Sensors detect flashes of light emitted by the diamond and send a signal to a microprocessor that fires a blast of air at the diamond, which spits it into a collection box.
Stage 5 – Cleaned, weighed, and packaged:
The diamonds collected in the recovery process are cleaned in an acid solution, washed, weighed, and packaged in sealed containers for transport. By the Kimberley process, these containers are sealed with a tamper-resistant seal, numbered on site, and a certificate of origin is issued.
You must be logged in to post a comment.