Martha Gold Mine Unique Open Pit Mining By Newmont

Martha gold mine constitute open pit mine that is very unique, located in the township of Waihi, New Zealand

Martha mines constitute open pit mine that is very unique, because the mining area is located in a residential area and near to a thriving community. With a population of about 4,700 people, the town of Waihi is situated on the east coast of the North Island of New Zealand.  Martha gold mine is  located in the township of Waihi, New Zealand. and owned by the Newmont Mining Corporation  a leading gold producer in the world.

Gold mining in Waihi has a history that spans three centuries. Gold was discovered in the 1800s and mined underground in the first half of the 1900s. The last 24 years of the 1900s focused on exploration

The Martha Mine has been operating since 1988. Martha gold mining project  was the first major hard rock mining operation to be commissioned following the resurgence of the gold mining industry in New Zealand in the late 1970s. The mining licence was granted for the open pit Martha Mine in 1987 and development and mining of the Martha Mine open pit. In the 2000s

Mineral Ore deposit in Martha gold mine New Zealand

The climate of Waihi is affected by its local topography. The rainfall in Waihi is relatively high, averaging in excess of 2,100 mm/year. Geology in waihi comprises predominantly rhyolite, with some dacite. The Waihi gold deposits are low sulphide epithermal gold-silver veins with associated volcanic breccias. The gold veins are hosted within a fine-grained volcanic rock, andesite, aged between 3 and 12 million years ago (Ma), during the Pliocene and Miocene.



MINING PROCESS IN MARTHA GOLD MINE NEW ZEALAND

Process blasting mining in Martha is a process of destruction and to excavate, break down or remove rock in the soil to rock minerals can be easily taken up and transported in Haul Truck

Martha gold mine is by open pit methods,  The early stages of the mining process in Martha gold mine is the process of drilling to insert explosives. Blasting in Martha gold mine is usually conducted between 7.00am -8.00am, 1.00pm - 2.00pm. 7.00pm - 8.00pm 

Before the blasting process in martha gold mine , to define the ore from the waste rock in mine area, rock samples taken from the area of the mine and then tested in the laboratory. Assay results are used to mark out areas of ore and waste rock, which are mined separately.

Process blasting mining in Martha is a process of destruction and to excavate, break down or remove rock in the soil to rock minerals can be easily taken up and transported in Haul Truck

Ore and waste rock are crushed at the surface facilities in the area mine later in the shovel and put into trucks,  Once the  capacity truck is full, the dispatch system directs the driver to the primary crushers

The crushing system at the Martha gold mine open pit consists of a combination of a jaw crusher and two Stamler feeder breakers.  Rock mineral is loaded into the crusher bin by trucks or loaders.

Two Stamler feeder breakers system

Jaw Crusher System

The jaw crusher operates by the mechanism of two large plates of steel moving towards each other on a cyclic basis to break rock from a large size to a smaller size. The jaw crusher is capable of crushing material with a strength of over 150 megapascals (MPa)

The Stamler feeder breakers are used to break moderately hard and soft material. A rotating drum covered with replaceable carbide-tipped picks serves to break the rocks, and feed the material along the conveyor underneath.

Conveyor on site transports the ore from the open pit
to the processing plant

There are a number of conveyors required to ensure that following crushing process, rock is transported to its correct destination. The main overland conveyor has a capacity of 6,000 tonnes per hour. This capacity makes it one of the largest mining conveyors in Australasia width of 1.35m and travels at a speed of 19 km/h.

In conveyor exist electromagnets at a number in points around the crushers and transfer stations to pick up steel, because the rock may contain steel and timber which can damage the conveyors.  The largest conveyor on site (the overland conveyor) transports the ore from the open pit to the processing plant, and the waste rock to the waste rock embankments.

The grinding process reduces the rock to a slurry in
Semi Autogenous Grinding (SAG) mill

Following crushing through a jaw crusher,  the ore is fed into the Semi Autogenous Grinding (SAG) mill  along with water, steel balls and the addition of lime to raise the pH of the ore. The grinding process reduces the rock to a slurry.

The slurry that remains after this process has a very fine particle size. Typically, 80% of the ore particles are less than 70 microns in size (about the same consistency as fine beach sand).

The remaining slurry passes through a pre-leach thickener , to remove some of the water. The recovered water is reused in the grinding circuit while the thickened slurry moves into the leaching circuit.

GOLD PROCESSING IN MARTHA GOLD MINE NEW ZEALAND

For gold leaching process,  Martha mine gold in the processing system using carbon in pulp. Fine particle size is required is required to cyanide leaching process.

Slurry from the process Semi Autogenous Grinding (SAG)

Slurry from the process Semi Autogenous Grinding (SAG) mill is then added a solution of sodium cyanide in leach tank. The tanks provide sufficient retention time to allow the gold and silver to be dissolved by the cyanide solution. Oxygen is added to assist in this process.

The slurry then moves through a series of carbon adsorption tanks . While the gold leaching process continues to run in this tank, the primary objective is to remove the gold and silver mineral from the solution. To achieve this, the carbon incorporated into the tank so that the gold and silver minerals bound in carbon

Carbon is heated to 600 degrees C for the recovery of most of the gold and silver solutions. And then put back into the first tank, because the gold and silver move towards the carbon via a diffusive process.

By the time the slurry reaches the final adsorption tank, most of the precious metals have been removed and wastes from pulp or commonly known as tailings is pumped to the tailings storage facility

carbon is then pumped to the elution circuit,  where the gold and silver is washed off with heated water and is passed to the electrowinning circuit. The remaining barren carbon is reactivated by acid washing and kilning and returned to the adsorption tanks

For the recovery of gold from the high-grade solutions  through a series of electrowinning cells, containing cathodes in the form of stainless steel plates. The gold and silver migrates and attaches itself to the stainless steel cathodes.

Cathode then rinsed with water spraying, and then the results of the water spray from the cathode in the form of silt mineral ores of gold and silver. When all the gold has been recovered from the solution, then solution is pumped back into the leach circuit.Then silt concentrat is dried , and then mixed with flux and inserted into a furnace for smelting process.

Smelting furnace for form bar of doré bullion

The smelting furnace attains a temperature of 1200 degrees C and after a few hours and materials melt to form a liquid metal look, the liquid metal is poured into molds produce doré bullion bars

The fluxes form a slag of impurities which is removed,leaving the bar that is pure molten metal content of 99% of the gold and silver. Each bar of doré bullion contains around 75% - 90% silver and 10% - 25% gold, and weighs approximately 20 kg.

The bullion from Martha gold mine is sent to the Western Australian Mint in Perth, where it is further refined to separate the gold from the silver. After refining, the gold and silver is credited to the Newmont Waihi Gold mine account and the precious metals are sent to the international market.