Page 301 - Introduction to Mineral Exploration

284 M.K.G. WHATELEY & W.L. BARRETT

drive, multipurpose drill rig. These holes,
drilled alongside established farm tracks over
the higher parts of the farm, proved that
rock, harder than could be penetrated with the
augers, existed at exploitable depths over an
area large enough to contain around 20 Mt of
material. The results from this drilling enabled
the geologists to establish overburden distribu-
tion, overburden types, water-bearing zones,
the depth of weathering, and the gradient of
the bedrock surface (Bell & Hopkins 1988). At
this stage there was no proof of the nature
of the harder material since no samples were
recovered. Nevertheless, it was assumed that
the impenetrable rock was markfieldite and,
although the drill pattern was irregular, it
showed that there was only thin overburden.
Geologists calculated the resources and over-
burden ratios for a theoretical quarry, and
within the margins of error in such calcula-
tions there appeared to be sufficient resources
for a viable quarry. The auger drilling in Phase
2 is estimated to have cost between £2000
and £2500.
FIG. 12.3 A top-drive, multipurpose, flight auger
drilling rig used to evaluate the resources on the
12.4 PHASE 3 – FEASIBILITY STUDY
Stud Farm property adjacent to Cliffe Hill Quarry.
Phase 3 of the Cliffe Hill Quarry project in-
cluded all the exploration drilling, a limited
amount of geophysics, the testing of the core purchase a brand new six cylinder, 100-hp top-
samples, the design of the landscaping works, drive, multipurpose, drilling rig (Fig. 12.3) to
the detailed specification of the processing evaluate fully the resource potential at Stud
plant, and the submission of the original plan- Farm. A rig of the type used, together with a
ning application, and a number of subsequent back-up vehicle and the relevant in-hole equip-
amendments to it, to the relevant local govern- ment, would have cost around £120,000, but
ment offices. this figure is included as depreciation in the
total drilling costs given below.
Drilling, using open-hole methods in the
12.4.1 Drilling
overburden and coring at various diameters in
The Estates and Environment Department of the bedrock, commenced in August 1979 and
Tarmac acts as a contract drilling company continued with some breaks until December
to the operating divisions and the Stud Farm 1989. During this period about 240 boreholes
work, although welcome, caused a number of totalling around 17,000 m were drilled, mainly
problems. With the continuing land acquisi- on a 50 × 50 m grid (Fig. 12.2). A planning
tion program rig-time was becoming scarce application for Stud Farm was prepared in
and although it had been hoped to undertake parallel with the exploration work.
any additional work at Stud Farm in-house, The experience gained while drilling the
the rapid exploration success meant that the original holes during Phase 2 indicated that
follow-up work could not be fitted into the certain aspects of the drilling would have to be
program of the existing, company owned rigs. improved if sufficient data were to be collected.
The company therefore took the decision to The indications were that there was between