Metallurgical accounting for base metal concentrates

A base metal concentrator may produce one concentrate or several from the same ore, such as a copper concentrate and a zinc concentrate, and a concentrate may carry precious metal credits or elements that a smelter charges for. Each product has to be balanced by mass and by each element, moisture affects the dry tonnes of every load, and concentrate stockpiled at site or in transit has to be accounted for. MAX has been used on a copper and zinc operation that tracked all of this in one system.

Feed, flotation and products

Ore is crushed, ground and floated, in one circuit or in several that produce one concentrate after another, with the remainder going to tailings. In MAX the feed, each concentrate, the tailings and the intermediate streams are measure points. Weightometers give feed tonnes, laboratory files give the assays, and formulas calculate dry tonnes, contained metal and recoveries for each element in each product, with explicit rules for how each figure rolls up from shift to month.

Payable and penalty elements

A concentrate’s value depends on its payable metals and on elements that attract smelter penalties. The copper and zinc operation that used MAX assayed nine elements on its products, including copper, zinc, lead, gold and silver as well as arsenic, cadmium, iron and mercury, so every load carried the full picture. Because each element is a separate measure, each can be balanced, trended and reported in its own right.

Moisture, loads and shipments

Concentrate is weighed wet but its metal content is calculated on dry tonnes, so MAX records moisture against every load. MAX tracks each truck load and shipment as a parcel with its wet mass, dry mass, moisture and assays, separately for each product, and records each transfer, so the path of every load is traceable. Shipments to sea can be recorded with their vessel, ports and bill of lading date, and split into consignments by consignee. A daily shipping report gives the logistics team the same figures as the plant.

Inventory and reconciliation

Concentrate held on site and in transit is inventory that has to be accounted for at each period end. MAX keeps these stocks as inventories with wet and dry mass, moisture and assays, and true them up against surveys. Period-end reconciliation distributes surveyed and shipped totals back across the month’s values, keeping each original value beside its reconciled value; the copper and zinc operation defined more than fifty reconciled figures this way and reviewed them in a dedicated reconciliation report.

Water, consumables and plant time

Flotation plants use water and reagents. Water, reagents and other consumables can be recorded in MAX alongside production, so consumption rates per tonne are calculated by the same formulas and reported in the same reports. Downtime is recorded against each item of plant, so availability and utilisation sit beside throughput and recovery.

Reporting

Daily process plant and company production summaries, a daily management report, a shipping report and a monthly budget and forecast variance report all come from the same database. Budgets and forecasts are imported by period, and variances show during the month rather than after it.