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Collection: Directories and Documents > Pamphlets
Mining Methods in Grass Valley District California From Transactions of the American Institute of Mining and Metallurgical Engineers by J A Fulton and A B Foote (PH 2-6) (1927) (14 pages)
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Page: of 14
658 MINING WHETSIODS IN, ands Vaux nysmagR, expronT
No regular method of caraaltlacy mill heads i ig in ge, pecnunel of ‘th x
erratic results obtained. The: tailings. from the stamp mill (cyanide i
heads) and the cyanide plant (final tails) are thoroughly. sampled and Ral
assayed daily. A close estimate of the daily production i is made from the ue
ounces of quicksilver fed in the mill each 24 hr, : Th) the cyanide nl antl Any
the number 0 of tons of solution precipitated ‘each: day i is lathe by Y
meter, and the value of the solution is: ‘determined by assay. Aeealt
Recently, some diamond drilling has been done, but nearly al explo 1.§
ing has been by drifts, shafts, crosscuts, ete. : 09..) sae at
Maps are brought up to date each month, and . ‘models lee vont, 0
Areas stoped and developed are measured on the maps, with a, planimeter; ene
this gives the usual unit Apures, for production and per centage, of i Prong
able ground. “a
Estimates are based “enti oly on, experience’ ‘Development . is argfully inspeeted and the various areas classified. as ore gr waste. The prgbie
duction and tonnage expected from the areas: ‘classed . ‘as ore are based on
units per square foot, which in turn are based ' on the records of the past. i
twenty years. Generally, the estimates are low as the areas classed ap. ae
‘ore bigye tobe larger than estimated: ‘No percentage ot variation can sf
History of Mining Methods .
The orebodies are very irregular’ in ‘shape ean occurrence} Ait ioe
one-third of the area of the yein explored has proyed profitable. No . ‘
reason, such as intersecting veins, dykes,’ or faults, has been discovered
for one portion of the vein being ore and another barren. ro
The minimum angle of flow of broken ore is 45° on the foot wall or 40°
in a chute with a plank bottom. . The angle can be: reduced to 35 if p.
small stream of water flows over the bottom of the chute. et tains Pye Miss
As the average thickness of the vein is only 16 in,, ‘while the prereee
width of stope is 42 in., it is necessary to handle aout twice 23 foal
waste as ore. The rook is hard; it requires 1.6 lb. of powder and 3 iy qh "
‘hole drilled for each ton of ore (and the resultant waste). at
At first, levels were run from 60 to 100 ft, apart on the vein 6 ora.
was shoveled, through “ passes,’ into cars of 001 pepe i bi:
ert
ft and run direct to the m! rs
Ese oon toe of vein ‘and cars of 1-ton capacity ato _ drifts are run 300 ft. a art on the A
used, These are g ete hauled by mules, from soven to came er nd
ing a train, These cars are loaded from ‘chutes bully os 1 du
dump into bins in the main shaft, from which the skips a é ‘ihe broken
The chutes are filled by cars of ‘1500-Lb. capacity, ain hic phic yun on
ore from the stopes is loaded by shovels or Scrapers: d eT hogs tracks
temporary tracks built along the face; a8 the Laie it tho ¢ chutes by i
are moved close up:' The loaded oars aro lowered into