Negative Stockpile Configuration

Null analyte values and unassigned contributor errors occur on process flows when an upstream stockpile in the supply chain goes negative for any reason.

Less obvious contributor calculation errors occur when flow-through plants (for example, crushers) are allowed to build up unrealistically high stock levels.

In addition to the basic contributor calculation issues, the calculation of contributor analytes is erroneous when material is upgraded in a mineral processing plant.

Null values and unassigned contributor errors can severely impact the calculated production: not only within MineMarket, but also in systems to which MineMarket data is exported.

There are many valid reasons for a stockpile's balance to go negative in MineMarket, including:

  • Weight determination or estimation errors
  • Moisture gain or loss
  • Handling losses
  • Contamination from other sources

Such gains and losses are usually corrected via survey and other reconciliation mechanisms. These corrections may be on an event basis (for example, stockpile empty), or periodic basis (for example, monthly survey).

Reconciliations and surveys cannot normally be done after every transaction, shift or day. The negative stockpile management functionality within MineMarket can manage null analyte values and contributor values in the period between surveys and reconciliations.

Stockpiles and Despatches

Null analytes and unassigned contributors can occur on a stockpile or despatch when:

  • The amount reclaimed is greater than the amount stacked on an individual stockpile.
  • The amount unloaded from a transport is greater than the amount loaded.
  • An upstream stockpile or transport goes negative.

Mineral Processing Plants

One of the main reasons for null analytes is due to the practice of modelling mineral processing plants and equipment (for example, dump hoppers) as stockpiles in MineMarket. There are three basic types of plant to be considered:

  • Type 1: Flow though plants (no inventory) with no upgrade process
  • Type 2: Flow though plants (no inventory) with an upgrade process
  • Type 3: Plants with inventory and an upgrade process
Type 1 and Type 2 Plants

While many mineral processing plants may have a small to medium circulating load, in most cases, such plants can be assumed to hold zero stock, both from customer and MineMarket inventory management perspectives. Some plant processes are also designed to modify material characteristics which alter product analytes. The following types of physical processes are in these categories.

Type 1 plants have no significant modification of material characteristics; for example:

  • Dump hoppers, diverters, conveyors
  • Crushers
  • Some crushing and screening plants

Type 2 plants modify material characteristics; for example:

  • Some crushing and screening plants
  • Wash plants
  • Concentrators

Allowing Type 1 and 2 plants to have large positive or negative stock balances in MineMarket establishes the main pre-condition for erroneous analyte calculations.

  • Negative plant stock balances: Null analytes and unassigned contributor errors occur when a plant 'stockpile' goes negative somewhere in the supply chain.
  • Positive slant stock balances: If allowed to build up a large positive stock in MineMarket, analyte values will also be in error. Although the plant does not hold any actual inventory, many analytes that have previously flowed through the plant will still be present in the MineMarket 'stockpile', and thus may corrupt the analyte calculations.

The effect of modifying material characteristics in Type 2 plants results in the different output streams requiring different analytes. For example:

  • Crushing and screening plants: For an iron ore plant, the feed consists of ore that has a fragmentation profile. The analytes (for example, Fe assay) may change with fragmentation size, such that separating material based on size also upgrades one of the output streams (for example, 'Lump' product typically has a higher Fe assay than 'Fines' product), which results in the analytes differing to the feed.
  • Concentrators: For a base metal concentrator (for example. Cu flotation concentrator), the analytes differ significantly from the feed analytes.
Type 3 Plants

Type 3 plants are more complex, such as smelters and refineries. These plants may contain large quantities of expensive metals within various sections of the plant. These metals must be accounted as inventory. An example of such a plant is a Copper Refinery tank house.

MineMarket currently models Type 3 plants as black box 'stockpiles' and while it is a valid concept to allow such plants to hold internal stocks, the simple stockpile model currently in use is not appropriate for such plants.

Negative Stockpile Management in MineMarket

Important: Users should accept full responsibility for maintaining realistic stockpile balances by calibrating weighing devices, adjusting truck factors, conducting stockpile surveys, and so on, when required. However, the following options aim to eliminate the incidence and impact of null analytes and unassigned contributors on stockpiles.

WAG, FIFO, and LIFO Stockpiles

MineMarket has the following options to manage negative WAG, FIFO, and LIFO stockpiles:

  • Previous Period WAG
  • Assume Null

Previous Period WAG can be used to calculate either contributor values and analyte quality, or just used to calculate contributor values (in which case, analyte quality is assumed from product specifications).

Assume Null can be used if no assumptions should be made about contributor values and analyte quality. Negative stockpiles will have unassigned contributors and unknown quality.

Default options can be configured for locations. The default options can be overridden for individual WAG, FIFO and LIFO stockpiles.

3D Stockpiles

MineMarket has a setting for whether contributor values and analyte quality are retained on negative batches. This setting is for each individual 3D stockpile. See Create a 3D Stockpile.

Despatches

Each loadable/unloadable part of a despatch (truck despatch, train wagon or rake, shipment hold, or service trip) is modelled in MineMarket as a moving stockpile.

A negative balance can occur on a despatch stockpile if the sum of the unloading transactions is greater than the loading transactions; for example, because of inaccuracies in measurement equipment.

MineMarket has a global setting for whether contributor values and analyte quality are retained for despatch stockpiles with a negative balance. See Specify Despatch Stockpile Settings.

Priority of Sample Data

The calculated analyte qualities are all Assume Source calculations.

If a sample is associated with a stacking/loading transaction, that sample data is considered when calculating the retained values for a negative stockpile.

Any sample data associated with a reclaiming/unloading transaction will override the transaction’s assumed analyte quality. This rule is applicable to all types of negative stockpiles.