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Gold Dore Bars from North Kivu: What 85-96% Purity Actually Means for Refineries at the Smelting Stage

When a buyer or trading company purchases gold dore bars from North Kivu, Democratic Republic of Congo, the quoted purity of 85% to 96% is not just a quality figure. It is a commercial variable that directly determines processing costs, refinery margins, loss allowances, and the final settlement price paid to the seller.

Many buyers, particularly those new to artisanal and small-scale mining (ASM) supply chains in Central Africa, treat purity as a simple multiplier. In practice, it is far more complex. Understanding the mechanics of what happens at the smelting and refining stage is essential for any buyer, trading house, or end-user refinery that wants to accurately model costs and avoid unexpected losses.

This explainer breaks down exactly what dore purity means in practical refinery terms.

1. What Is Gold Dore, and Why Does North Kivu Dore Vary in Purity?

Gold dore is an unrefined alloy of gold and silver, sometimes containing trace amounts of copper, iron, lead, zinc, bismuth, and other base metals. It is produced at or near the mine site by melting down the gold concentrate or amalgam recovered during artisanal processing.

In North Kivu, artisanal miners work across a range of geological settings, from alluvial river deposits to hard-rock quartz veins. The resulting dore varies in composition depending on:

• The ore body type and associated mineralogy
• The smelting equipment and process used at the mining site
• The skill of the local operator and the quality of fluxes used
• The degree to which silver and base metals have been removed prior to casting

This is why North Kivu dore typically ranges from 85% to 96% gold, with the remainder being primarily silver and minor base metal impurities. A bar from an alluvial deposit near the Ulindi River may test at 91%, while a hard-rock bar from near Walikale may come in at 87% due to higher silver content in the ore.

The variation is not a defect. It is an inherent characteristic of artisanal dore production, and professional buyers and refineries are well-equipped to handle it. However, the purity point matters enormously in determining what the bar is worth.

2. What Happens to Dore at a Refinery: The Smelting Stage Explained

When dore arrives at an accredited refinery, the processing sequence typically follows these stages:

Assaying

The first step is fire assay or X-ray fluorescence (XRF) analysis. The refinery takes samples from multiple points in the consignment to determine the precise gold, silver, and impurity content. This assay result is the basis for the entire financial settlement.

It is important to note that the assay result at the refinery may differ from the seller's pre-shipment assay. Refineries apply their own analytical standards and will use their certified assay for settlement purposes.

Melting and Smelting

The dore is melted in induction or gas-fired furnaces. During this stage, base metal impurities with lower melting and boiling points begin to volatilize or oxidize and are removed as slag. This process reduces the non-gold content of the material.

The resulting material is a more purified alloy, but it is still not .9999 fine gold. Further refining is required.

Refining to Fine Gold

The refinery then uses one or a combination of:

• The Miller Chlorination Process: chlorine gas is bubbled through molten gold to remove silver and base metals as chlorides
• The Wohlwill Electrolytic Process: electrorefining that produces .9999 fine gold
• Chemical leaching methods: for lower-grade or more complex feeds

For standard commercial dore in the 85-96% range, the Miller Process is typically used first, followed by Wohlwill electrolysis to achieve investment-grade purity.

3. The Purity Percentage and What It Actually Represents

When we say a bar is 90% pure gold, we mean that in every 100 grams of dore, there are approximately 90 grams of gold and 10 grams of other material (silver, copper, base metals).

However, the refinery does not simply pay for 90% of the gold spot price. The calculation is more nuanced and involves several deductions. Understanding each deduction is critical.

Indicative Breakdown of a 1 kg Dore Bar at Three Purity Levels

Parameter	85% Purity Bar	90% Purity Bar
Total bar weight	1,000 g	1,000 g
Gross gold content	850 g	900 g
Silver content (est.)	120 g	80 g
Base metal impurities	30 g	20 g
Net payable gold (after losses)	~832 g	~882 g
Note	Higher processing load	Standard refinery feed

Note: The above are indicative figures. Actual refinery calculations will differ based on specific assay results and contractual terms.

4. Loss Factors: The Critical Variable Most Buyers Overlook

Loss factors are percentage deductions applied by the refinery to account for:

• Metal mechanically lost during handling, sampling, and melting (spillage, fume, dust)
• Metal chemically lost during processing (slag entrapment, incomplete chlorination)
• Refinery margin and operational costs embedded in the loss factor

Loss factors typically increase as dore purity decreases. This is because lower-purity material contains more impurities that must be removed, requiring more intensive processing and generating more by-product streams in which gold can be mechanically or chemically trapped.

Typical Loss Factor Ranges for Dore

Dore Purity Range	Typical Refinery Loss Factor	Effective Gold Recovery
96% - 99%	0.5% - 1.0%	99.0% - 99.5%
91% - 95%	1.0% - 1.5%	98.5% - 99.0%
85% - 90%	1.5% - 2.5%	97.5% - 98.5%
Below 85%	2.5% - 4.0%+	96.0% - 97.5%

These figures are illustrative. Each refinery publishes its own treatment schedule. London Bullion Market Association (LBMA)-accredited refineries are required to maintain transparent and auditable loss accounting.

Critically, a buyer purchasing 85% dore and expecting to lose only 1% at the refinery will be financially surprised. The actual loss on a low-purity bar may be 2% or more of the gold content. On a large consignment, this difference can amount to tens of thousands of dollars.

5. Refinery Treatment Charges: How Purity Affects What You Pay

In addition to loss factors, refineries charge treatment fees (also called smelting and refining charges, or TC/RC). These are typically structured as:

• A flat per-troy-ounce fee for refining services
• A base metal penalty per unit weight of specific impurities
• A minimum charge per consignment regardless of weight

Lower purity dore generates higher treatment charges in two ways. First, the refinery must process more impurity volume for the same amount of gold. Second, penalty charges for base metals (copper, lead, bismuth, zinc) are applied based on the impurity content revealed in the assay.

Example: Treatment Charge Comparison

Charge Component	90% Purity Bar	85% Purity Bar
Base refining charge	USD 1.50/troy oz	USD 1.50/troy oz
Base metal penalty (copper)	Nil	USD 0.40/troy oz
Complex feed surcharge	Nil	USD 0.30/troy oz
Total charge (approx.)	USD 1.50/troy oz	USD 2.20/troy oz

Note: Charges are illustrative only and will vary by refinery and contractual terms.

For a consignment of 500 troy ounces, the difference in treatment charges between a 90% bar and an 85% bar could exceed USD 3,500 in this example. Multiplied across multiple shipments over a year, the financial impact is substantial.

6. The Settlement Calculation: How the Final Price Is Determined

The final settlement for a dore purchase is calculated as follows:

Step 1: Assay-certified gold content (grams or troy ounces)

Step 2: Apply the refinery loss factor to determine payable gold

Step 3: Apply the refinery outturn percentage (typically 99.0% to 99.5% for standard dore)

Step 4: Multiply payable gold by the agreed gold price (LBMA AM or PM fix, or spot)

Step 5: Deduct treatment and refining charges

Step 6: Deduct any applicable penalties for base metals or contaminants

Step 7: Net settlement = amount paid to seller (or amount payable to buyer if structured as a purchase)

Worked Example: 10 kg Consignment at 90% Purity

Item	Value
Total bar weight	10,000 g (321.5 troy oz)
Gold content at 90% assay	9,000 g (289.4 troy oz)
Less: 1.5% refinery loss	133.5 g (4.3 troy oz)
Payable gold	8,866.5 g (285.1 troy oz)
Gold price (LBMA PM fix example)	USD 2,400 per troy oz
Gross value	USD 684,240
Less: Treatment charges (USD 1.50/oz)	USD 427.65
Net settlement to seller	USD 683,812.35

Note: Gold price and charges are for illustrative purposes only. Actual settlement terms depend on the contract between buyer and refinery.

7. Silver Credit: A Partially Offsetting Factor

A point often missed in commercial negotiations is that silver present in dore is recoverable and commands a credit. Silver in North Kivu dore is typically present in concentrations of 3% to 12% depending on the ore source.

Refineries will assay the silver content and apply a silver outturn at a lower recovery rate than gold (typically 95% to 98% for silver). The resulting silver credit is calculated as:

Silver credit = payable silver (troy oz) x silver spot price x agreed percentage (usually 95% to 98%)

For a bar with 8% silver content by weight, the silver credit can partially offset higher treatment charges. Buyers should factor silver credit into their landed cost models, particularly for lower-purity dore where silver concentrations may be higher.

8. The Commercial Implications for Buyers of North Kivu Dore

Understanding the mechanics above leads to several direct commercial implications for any buyer procuring from North Kivu:

Do Not Price Solely on Headline Purity

Two bars, one at 90% and one at 85%, are not simply 5% apart in value. The 85% bar will incur higher loss factors, higher treatment charges, and potentially base metal penalties. The all-in cost differential may be 7% to 9% when fully modeled.

Verify the Assay Methodology

Ensure that the seller's pre-shipment assay uses a recognised methodology (fire assay is preferred over XRF for settlement purposes). Discrepancies between the field assay and refinery assay create settlement disputes and can erode margins

Understand Your Refinery's Treatment Schedule

Every LBMA-accredited refinery publishes a fee schedule. Before committing to a purchase, model the refinery charges against the expected purity range of the consignment. Do not assume a single flat rate applies.

Account for Transit Losses and Minimum Charges

Many refineries apply minimum consignment charges. Small consignments of dore (below 5 kg gold equivalent) may face disproportionately high per-ounce costs due to fixed minimum charges. Buyers should aggregate shipments where operationally possible.

Build a Purity Tolerance into Purchase Contracts

When contracting to buy North Kivu dore at an agreed purity range, include provisions for price adjustment if the assay result falls outside the agreed range. This protects both buyer and seller from unexpected financial outcomes.

9. Compliance Context: Why Responsible Sourcing Matters in This Calculation

North Kivu is a conflict-affected region under the scope of the OECD Due Diligence Guidance for Responsible Supply Chains of Minerals from Conflict-Affected and High-Risk Areas (CAHRAs). Buyers sourcing from this region are required to conduct risk-based due diligence across their supply chain.

This compliance requirement has a direct bearing on refinery access. LBMA-accredited refineries and other responsible smelters will require:

• Documentation of the mineral's provenance and chain of custody
• Evidence of due diligence conducted by the buyer under OECD or equivalent standards
• Country-of-origin declaration and, where applicable, ICGLR Regional Certification Mechanism (RCM) or iTSCi traceability documentation

Buyers who cannot provide adequate compliance documentation may find themselves limited to non-LBMA refineries, which may offer less favourable treatment terms or lower gold recovery rates.

At East Africa Plus Minerals, all mineral exports are handled with full compliance documentation, chain of custody records, and traceability reporting aligned with international due diligence standards. This ensures that buyers can present their refinery with complete documentation packages and access the best available treatment terms.

10. Summary: What Buyers Should Know Before Committing to a Purchase

Factor	85% Purity	90% Purity	96% Purity
Gross gold content (per kg)	850 g	900 g	960 g
Typical loss factor	1.5% - 2.5%	1.0% - 1.5%	0.5% - 1.0%
Relative treatment charge	Higher	Standard	Lower
Silver credit potential	Higher	Moderate	Lower
Base metal penalties	More likely	Possible	Unlikely
Complexity for refinery	High	Medium	Low