Ore-sorting is a process for upgrading mineral bearing rock. Current technology supplies two different types of ore sorting: Bulk and Particle . Current studies indicate the CuMo will most likely use both types of sorting in order to improve mill feed grades and potentially lower costs.
Bulk sorting involves scanning crushed material on a conveyor belt or within a shovel load, using various scanning techniques to identify the grade of bulk sections of the mined material. For example, bulk sorters are currently in operation that can scan material crushed at 60 mm size (2.5 inches) at the rate of 5,000 tons per hour using Proton Neutron Gamma scanner (PGNAA). This allows the feed to be divided into blocks /packets of various sizes depending on the width and speed of the conveyor belt and the scan time. The material can then be separated using flow diverters into three grades waste, middling’s and mill feed. Middling’s can be forwarded for additional finer level sorting.
Particle sorting is typically between 250mm and 10mm (1 to 4 inches) and involves evaluating the mineral content of individual rocks as they pass through a sensor then separating them into Accept and Reject fractions, based on pre-determined selection criteria.
Ore-Sort – General
Ore-Sort – Tungsten
Geologists have known for years that the grade at CuMo is contained in narrow stockwork veins, with the number and width of these veins controlling the grade. The more veins and/or thicker the veins the better the grade.
Geological zones vary from 0% to 40% of the material containing the grade. The example below contains a drill intersection on the edges of the molybdenum core zone. Use the radio buttons to turn the sorting on and off.
The section from Hole 11-59 from 1630 to 1640 feet assayed 0.175% Mo
Approximately 10% of the interval contains the actual molybdenum veins which are dark grey to black in the picture. The box length is 2 feet long. Breaking it into to 2 to 3 inch pieces is done to simulate primary crushing. Sorting would initially identify the ore (red – 22.5%) within the interval and that would be mill feed, secondary sorting would identify the stockpile (yellow – 30.5%), and remaining material is waste (blue – 47%). This would result in a grade of 0.583% Mo for the mill feed, and 0.134% Mo for the stockpile.
In the recent SRK PEA report, in a 2017 analysis of Ore Sorting conducted by sacre-davey, both bulk and particle sorting were analyzed, and a three-stage bulk sort followed by a particle sort was recommended. The analysis was based on a very coarse 10-foot sample distribution as further work is required to fully utilize the three (3) inch material size. The result show that an approx. 122% increase in grade is predicted for the 10-foot sample interval while preliminary testing on the particle sorting indicates a 240% increase in grade can be suggested.
The initial bulk sort would sort the feed at rate of 5,000 tons per hour with a 30 second scan time. This result in a sorting packet size of 42 tons, the middling’s from this sort and passed to slower moving stage 2 which operates on 2,500 tons per hour resulting in a packet size of 20 tons, the final bulk sort is fed at 1,250 tons per hour for a packet size of 10 tons. The middling’s from the bulk are then feed through a particle sorting system that separates individual rock pieces at 1 to 3 inch size range.
Further work is ongoing on improving the sorting and possibly reducing the number of sort stages as well as possibly improving the grades to levels reported by the particle sorting preliminary.