Applied Clay Mineralogy Phần 5 potx

the wider spaced drilling indicates that the size and quality of the deposit is

sufficient to warrant mining, then close spaced drilling is done (Table 10).

The information from the auger and core drilling provides the thickness

and type of overburden and the quality and thickness of the kaolin, so that

the stripping ratio can be determined. The stripping ratio is the overbur￾den thickness over the kaolin thickness. Stripping ratios determine

whether or not mining the deposit is economical. The lower the ratio, the

lower the cost of mining. The drilling program also is used to evaluate

potential groundwater problems if the water table is high or if there is

artesian water in sand bodies immediately under the kaolin bed. In kaolin

or bentonite deposits of hydrothermal origin, the drill hole locations are

based on the topography and shape and size of the alteration zone. Fig. 23

shows the configuration of a hydrothermal kaolin deposit in the Cornwall

area of southwestern England, which requires a special drill hole pattern

to delineate the deposit.

Flat lying bentonite deposits are also drilled using a grid pattern, but if

the deposits are steeply dipping or structurally deformed, then special

drilling patterns are used. Auger drilling bentonite deposits are much

more commonly used than core drilling. The same is true for drilling

palygorskite and sepiolite deposits. Normally, the palygorskite and

sepiolite deposits are flat lying as are ball clay deposits. They are sedi￾mentary clays that were deposited in lacustrine, swamp, or tidal flat

environments, and are located in areas that have not been deformed by

mountain building, faulting, and folding.

1. KAOLIN MINING AND PROCESSING

Once a mine plan has been determined after the drilling is completed,

the land is cleared and the removal of overburden begins. Open pit

methods of mining are used in the major kaolin deposits around the

world. A variety of stripping methods is used including hydraulic back￾hoes and shovels which load directly into large off-road trucks; pan-type

self-loading scrapers that are sometimes pushed by dozers if the over￾burden dirt is wet or relatively dense; large draglines which dump the

spoil into the previously mined out panels; and bucket wheel excavators

loading the spoil on conveyor belts. This latter method is sometimes used

in Europe.

After the overburden is removed, the kaolin is mined (Murray, 1963)

using much the same methods that are used to remove the overburden.

However, the mining must be done with much more care to assure

68 Applied Clay Mineralogy