EM 10: Aqueous (Surface mining

Suraface Mining

Mechanical Excavation, Aqueous

Underground Mining

Supported, Unsupported, Caving

Mechanical Excavation

Employs mechanical processes in a nominally dry environment to free minerals from the earth.

Aqueous Mining

Uniquely reliant on water or an aqueous mixture during mining and processing to recover the valuable mineral by jetting, slurrying, dissolving, or melting. Account for about 10% of surface mineral production.

Solution or Placer Mining

two types of Aqueous mining

Solution mining

Minerals are recovered through dissolution, leaching, slurrying, or melting processes.

3 Categories:

BOREHOLE EXTRACTION SYSTEMS

LEACHING METHODS

EVAPORITE/EVAPORATIVE PROCEDURES

Borehole extraction

Extraction through injection of fluids and raising the pregnant solution through boreholes or wells.

Sulfur wells

an application of borehole extraction under solution mining

reqs:

1. A large deposit of >5% sulfur

2. An adequate and inexpensive supply of water

3. A low-cost source of fuel to heat the wate

1. Preparing the solution by heating or adding the proper lixiviant

2. Pumping the solution into the deposit to bring the valuable mineral into the solution (by melting, dissolution, or slurrying)

3. Raising the pregnant solution (or slurry or molten material) to the surface

Cycle of operations under Borehole extraction

be ore strength

reasonably competent, but porous and permeable

be rock strength

competent and impervious

be deposit shape

any, but prefer tabular w/ large extent

be deposit dip

any, but prefer flat or low

be deposit size

moderate to large, thickness >50 ft (15 m)

be ore grade

intermediate (sulfur > 5%

be ore uniformity

variable to uniform

be depth

intermediate to high

LEACHING

• Applicable to soluble or leachable ore deposits, usually a secondary mining process.

• The chemical extraction of metals or minerals from the confines of a deposit or from material already mined

In-situ leaching

extraction is carried out on mineral in place

Heap leaching

performed in previously mined dumps, tailings, or slag piles

Vat leaching

performed in vats or tanks, uses the flooded leaching procedure

Heap leaching

• Accomplished by the percolation of the lixiviant through broken ore mass.

• Impermeable rubber lining, maximum 3° slope.

Water

Potash/Trona lixiviants

Gold, Silver

NaCN

SEA WATER, LAKE BRINE PROCESSING

Magnesium

l ore strength

permeable or rubblized material

l rock strength

ca n be wea k but must be impervious to fluid tra nsport

l DEPOSIT SHAPE

ma ssive or la rge vein

l deposit dip

steep, if a vein

l deposit size

any, prefer large

l ore grade

ca n be very low

l uniformity

variable

l depth

depends, typica lly < 300 m

Placer Mining

Recovery of heavy minerals from alluvial or placer deposits using water to excavate, transport, and/or concentrate the mineral

2 Types: HYDRAULICKING DREDGING

Placer deposit

any concentration of minerals that has been redeposited in unconsolidated form by the action of a fluid

ALLUVIAL, EOLIAN, MARINE, GLACIA (AEMG)

Classification of Placer Deposits

1. Material amenable to disintegration by the action of water under pressure

2. Adequate water supply available at the required head

3. Adequate space for waste disposal

4. Difference in density, or a similar property between ore minerals and gangue to allow efficient minerals processing

5. Natural gradient amenable to hydraulic transport of mineral (if hydraulicking)

6. Ability to comply with environmental regulations

Placer mining properties

h ore grade

heavy minerals in unconsolidated soil / gravel w/ minimum boulders

h ROCK STRENGTH

: unconsolidated

h deposit shape

placer type, tabular, bank or bench

h deposit dip

nea rly fla t (2-6% gra de)

h deposit size

small to intermediate (thickness 5-60 m)

h ore grade

can be very lowh

h ore uniformity

fairly uniform

h depth

very shallow, little overburedr

dredging

The underwater excavation of a placer deposit, usually carried out from a floating vessel called a dredge

Can be classified into: SHALLOW-WATER METHODS DEEP-SEA METHODS MARINE MINING METHODS

Mechanical dredges

Mechanically excavate and transport the material. e.g. dipper, bucket, ladder dredges

Hydraulic dredges

Designed to transport the mineral in slurry form, using water as the transport medium.

d ore deposit

unconsolidated deposit

d ore strength

unconsolidated

d deposit shape

placer type, tabular, bank or bench

d deposit dip

prefera bly fla t (2-6% gra de)

d deposit size

dintermediate to large (thickness 8-60 m)

d ore grade

ca n be very low

d ore uniformity

fairly uniform

d depth

very shallow, littleoverburden