Gold Milling Operations at Snip Mine

Gold Milling Operations at Snip Mine

Exploration and staking in the area commenced as early as 1929. The original Snip showing was located by Cominco geologists in 1965. The property changed hands in the 1970’s but was reacquired by Cominco in 1980 only to be optioned to Delaware Resources cum Prime Resources in 1986. Exploration drilling and underground sampling from 1986 to 1988 indicated the presence of a significant gold deposit. Detailed underground drilling and bulk sampling in 1989 confirmed the presence of a mineable deposit.

Metallurgical Testwork

Gravity Circuit

The objective of the testwork in the proposed gravity circuit was to:

a) Determine if sufficient free gold could be recovered to make the installation worthwhile.
b) Establish whether a gravity concentrate of refinable grade could be produced.

Cyanidation Circuit

Objectives were to establish

a) Optimum grind.
b) Leach plant feed density.
c) Leach circuit retention time.
d) Reagent selection and consumption.
e) Pre-aeration requirements.

Flotation Circuit

a) Recovery.
b) Concentrate grades.
c) Retention time.
d) Reagent selection and consumption.
e) Concentrate regrind requirement.
f) Concentrate cleaning circuit requirement.
g) Conditioning requirement.

Design Criteria

Crushing Plant targeted operating rate to produce 80% minus feed was from 40 to 50 tonnes per hour of new feed. Screen capacity on the 4×8 unit was estimated at 40 tonnes per hour. Plant throughput has since proven to be in the 40 to 50 tonne per hour range depending on fines and moisture content.

The 7×7 primary mill that came with the used plant was too small and was replaced with a new 8 x 12, 400 hp Boliden Allis mill. The 7×7 used mill, complete with motor and drive, is being used to grind mine waste for incremental backfill.

The 18 x 24 duplex jig that came with the plant was replaced with a larger 24 x 24 Duplex Yuba Richards jig. This unit has proven to be an extremely reliable, effective and forgiving piece of equipment. Also included in the gravity circuit is a smaller 12 x 24 Duplex Yuba Richards cleaner jig to minimize loading to the full size Concenco Deister table. Theoretically a smaller table could have been utilized but would have been a mistake.

Again refining has proven to be a learning experience. Current gold fineness in the bullion bars is running between 750 and 800 Au. Impurities are averaging 5 to 6% most of which is lead. Conventional reagents being used include nitre, fluorspar, silica, borax and soda ash. However the nitre required is much higher than anticipated as is the ratio of flux to gravity concentrate (4:1).

Considerable difficulty was encountered both in the bench scale testwork and the pilot mill work in making a targeted float concentrate grade of 360 to 400 grams/tonne. More and more cleaner and recleaner capacity was built into the plant design.

 

The capacity of the 12 foot concentrate thickener included in the used mill at a milling rate of 300 tpd was estimated 6.8 square feet per ton per 24 hours. At current production rates the capacity has dropped to 4.5 square feet per ton of float concentrate per 24 hours which is borderline. Flocculant is being used.

Filter capacity was predicated on 2 square feet of filter area per ton of concentrate per 24 hours. The used unit was operating to 74% of capacity at a mill feed rate of 300 tonnes per day. At current feed rates the double disc 4 foot unit is overloaded at 113% of capacity.

Services

Power is supplied from four 880 kw diesel generators two of which are running at any one time. Waste heat is recovered from the diesel engines to supply building heat and hot water. Two diesel-fired boilers are in place as backup and to supply incremental building heat as required.

gold-millings tailings impoundment

gold-millings flowsheet

gold-millings backfill plants

gold-millings cross sections

gold-millings liner extension detail

gold-millings effluent treatment schematic

gold-millings pond dimensions

gold-millings location of property

gold milling operations at snip mine