Read the text carefully and answer questions 11-15 below.

UNDERGROUND HARD ROCK MINING SUBSIDENCE

http://www.nswmin.com.au

When there are low concentrations of minerals in the ore body,

large amounts of ore need to be extracted and processed for the

mine to be economical. This can be done through open cut methods

or underground methods, with the appropriate method depending

on local circumstances, such as the depth of the ore body. ⁵

Some of the underground methods used to extract large volumes

of ore include block caving and panel caving. Each of these methods

involves tunneling under the ore body, fracturing the overlying ore

body and allowing it to cave down through gravity to underground

draw points where it can be extracted for processing. ¹⁰

When the ore body caves down, the overlying rock subsides

forming a subsidence zone at the surface. At the surface, the subsi-

dence zone will typically take the shape of a cone of depression with

steep slopes at the edges. There may also be some surface cracking

around the edges of the subsidence zone. The area and depth of ¹⁵

the subsidence zone will depend on the local conditions, such as the

amount of ore extracted and the nature of the local geology.

Access to the subsidence zone is restricted and any built or natural

features in this zone will generally be lost. Impacts caused by sub-

sidence are fully assessed during the project approval process with ²⁰

appropriate measures implemented to minimize or offset any impacts.