3. Revenue

The Company derives its revenue from the sale of doré and concentrate. The following table presents the Company’s net sales disaggregated by source:


	Three months ended June 30,				Six months ended June 30,
	2018		2017		2018		2017
	(in thousands)				(in thousands)
Doré sales, net
Gold	$	1,722	$	1,435	$	3,631	$	3,062
Silver		472		21		769		42
Less: Refining charges		(38)		(5)		(63)		(22)
Total doré sales, net		2,156		1,451		4,337		3,082
Concentrate sales
Gold		5,396		4,514		10,937		11,600
Silver		8,803		5,604		14,884		12,892
Copper		2,638		1,219		5,018		2,529
Lead		3,498		2,316		7,345		4,254
Zinc		11,841		7,790		25,225		13,846
Less: Treatment and refining charges		(1,261)		(1,479)		(3,095)		(2,987)
Total concentrate sales, net		30,915		19,964		60,314		42,134
Realized/unrealized embedded derivative, net		(2,303)		(24)		(1,732)		511
Total sales, net	$	30,768	$	21,391	$	62,919	$	45,727

Doré Revenue

Doré sales are recognized upon the satisfaction of performance obligations, which occurs when control of the doré transfers to the customer. Transfer of control occurs once the customer takes possession of the doré. Doré sales are recorded using quoted metal prices, net of refining charges.

Concentrates Revenue

Concentrate sales are initially recorded based on 100% of the provisional sales prices, net of treatment and refining charges, at the time of delivery to the customer at which point the performance obligations are satisfied and control of the product is transferred to the customer. Adjustments to the provisional sales prices are made to take into account the mark-to-market changes based on the forward prices of metals until final settlement occurs. The changes in price between the provisional sales price and final sales price are considered an embedded derivative that is required to be separated from the host contract for accounting purposes. The host contract is the receivable from the sale of the concentrates at the quoted metal prices at the time of delivery. The embedded derivative, which does not qualify for hedge accounting, is adjusted to market through revenue each period prior to final settlement. Market changes in the prices of metals between the delivery and final settlement dates will result in adjustments to revenues related to previously recorded sales of concentrate. Sales are recorded net of charges for treatment, refining, smelting losses and other charges negotiated with the buyer. These charges are estimated upon delivery of concentrates based on contractual terms and adjusted to reflect actual charges at final settlement. Historically, actual charges have not varied materially from the Company’s initial estimates.