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Rain can change feed moisture, clay behaviour, access and the amount of water a gold plant must manage. It does not mean the ore has automatically become poorer, and a loss in recovered gold should not immediately be blamed on the concentrator. First establish whether the change is in feed quantity, grade, preparation or the process itself.
This guide helps alluvial operators organise that investigation and prepare for wet conditions. The useful outcome is a feed and water-management plan supported by observations and sampling, rather than a universal instruction to add a scrubber.
Measure what changed
Record delivered feed, operating hours, moisture where relevant, grade samples and product output. Wet truck tonnes are not dry solids tonnes, and loose cubic metres do not convert to tonnes without a measured density basis. Changing measurement methods during the rains can make apparent recovery trends misleading.
For an illustrative truck load of 20 wet t at an assumed 15% moisture by wet mass, dry solids are 20 × 0.85 = 17 t. Applying a grade expressed per dry tonne to all 20 t would overstate the gold input. Replace the moisture assumption with an appropriate measurement programme.
Distinguish washing from difficult scrubbing
Observe whether gold-bearing fines remain attached to oversize or locked in clay lumps after the existing washing step. Sample rejected material and investigate its gold content. A larger screen opening or more water can change throughput while still sending recoverable gold to reject.
McLanahan’s rotary-scrubber guidance explains that tumbling can remove some clays but that tough plastic clays can behave differently, including pelletising. Trial actual material before selecting the washing duty. “Clay present” is not enough information to choose equipment.
Match classification to the recovery circuit
Specify the size and flow that the downstream sluice or concentrator is designed to receive. Check screen performance on wet, variable feed and investigate blockage or bypass. Changing a screen to raise nominal capacity can move the bottleneck or alter the particle distribution reaching recovery.
SGS’s gravity-separation reference highlights the role of size preparation. Use feed, oversize, concentrate and tailings samples to identify where gold is leaving the circuit, rather than relying on visible gold alone.
Review the complete water balance
Separate clean runoff from process water where the design permits, protect stockpiles and direct drainage according to the engineered site plan. Check pump duty, return-water quality, storage, erosion and conditions for discharge. Stormwater reaching a process pond adds an operating and containment load; it is not simply free makeup water.
Have the relevant specialists assess storage capacity and abnormal conditions. The IFC management framework is a useful reference for connecting changing site risks to responsibilities and monitoring, alongside project approvals.
Prepare equipment and the operating response
Inspect drainage, pumps, standby power, roads and stockpile arrangements before the wet period. Agree who decides to reduce feed or stop when water, ground conditions or equipment exceed the approved operating limits. Check that operators can communicate those conditions and that maintenance spares are available.
Use a staged trial if the feed-preparation circuit needs modification. Record the settings, sample streams and actual throughput so the result can be compared with the previous configuration. Our alluvial cost examples distinguish a wash-and-sluice scope from scrubber-based proposals.
Questions and answers
Does lower gold output after rain prove that the concentrator needs replacing?
First compare dry feed, grade, operating hours, preparation and the sampled loss streams. Rain can change moisture, clay, access and water management, so the apparent shortfall may have more than one cause. Use those observations to identify a trial or correction before buying a different recovery machine.
Can I restore performance simply by increasing washing water?
Check the washing, classification and downstream recovery duties together. More water can change flow without freeing gold from difficult clay or preventing losses to oversize. Trial representative wet-season feed and review the site's water balance so the proposed change improves the measured constraint within the designed operating conditions.
Trace the loss before changing the plant
Measure feed consistently, investigate clay and classification, and review the water system as a whole. Select changes from representative trials and a site plan that remains workable in wet conditions. Your next step is a documented wet-season inspection and sampling programme that identifies the actual constraint.
Sources and assumptions
Manufacturer and technical references were reviewed on 5 October 2026. The moisture calculation is illustrative. This guide sets no rainfall design event, pond capacity or guaranteed recovery.