7. Property, Plant and Equipment, Net

The components of property, plant and equipment are as follows:


	June 30,		December 31,
	2017		2016
	(in thousands)
Mineral properties	$	9,352	$	9,352
Exploration properties		2,518		2,518
Royalty properties		200		200
Buildings		4,221		4,386
Mining equipment and machinery		16,055		16,351
Other furniture and equipment		952		952
Asset retirement cost		865		992
		34,163		34,751
Less: Accumulated depreciation and amortization		(25,454)		(25,516)
	$	8,709	$	9,235

The asset retirement cost (“ARC”) is all related to the Company’s Velardeña Properties. The decrease in the ARC during the period is related to an adjustment to the asset retirement obligation (“ARO”), as discussed below in Note 9.

In August 2016, the Company sold certain mining equipment consisting of two haul trucks, two scoop trams and a compressor to Minera Indé, an indirect subsidiary of Sentient, for $687,000 (see Note 20). The equipment sold was excess equipment held at the Company’s Velardeña Properties that the Company did not expect to use. The Company received $69,000 or 10% of the sales price at the closing of the sale, with the remaining $618,000 plus interest on the unpaid balance at an annual rate of 10% due in February 2017. The Company and Minera Indé amended the original equipment sale on March 31, 2017 to include the sale of an additional piece of excess equipment for $185,000 and extend the time for payment relating to the original equipment sale. Upon execution of the amendment the Company received an additional payment of $100,000. The remaining principal and interest balance, plus additional interest on the unpaid balance at an annual rate of 10%, was amended to be due in August 2017. The Company recorded a gain of $105,000 on the sale of the additional equipment, included in “Other operating income” in the accompanying Condensed Consolidated Statements of Operations and Comprehensive Loss, equal to the gross proceeds less the remaining basis in the equipment. On May 2, 2017, the Company received approximately $750,000 from Minera Indé as payment in full for the remaining balance due related to the equipment sale, including interest through that date.

In the third quarter 2016, the Company, through its wholly owned Mexican subsidiary, entered into an earn-in agreement with a 100% owned Mexican subsidiary of Electrum Global Holdings, L.P., a privately owned company (together “Electrum”), related to the Company’s Celaya exploration property in Mexico. The Company received an upfront payment of $0.2 million and Electrum has agreed to incur exploration expenditures totaling at least $0.5 million in the first year of the agreement, reduced by certain costs Electrum previously incurred on the property since December 2015 in its ongoing surface exploration program. Electrum, at its option, can elect to acquire an undivided 60% interest in a joint venture company to be formed to hold the Celaya project after incurring exploration expenditures totaling $2.5 million during the first three years of the agreement. Electrum would serve as manager of the joint venture. If we elect not to contribute to additional exploration or development expenditures after the initial earn-in period, Electrum, at its option, would have the right to earn an additional 20% interest in the Celaya project, for a total interest of 80%, by incurring an additional $2.5 million of exploration or development expenditures over a second three-year period. Following the second earn-in period we would have the right to maintain our 20% interest or our interest ultimately could be converted into a 10% net profits interest.

In April 2016, the Company entered into an option agreement under which Santacruz Silver Mining Ltd. (“Santacruz”) may acquire the Company’s interest in certain nonstrategic mineral claims located in the Zacatecas Mining District, Zacatecas, Mexico (the “Zacatecas Properties”) for a series of payments totaling $1.5 million. Santacruz paid the Company $0.2 million on signing the agreement, and another $0.2 million and $0.3 million in October 2016 and May 2017 respectively. To maintain its option and acquire the Zacatecas Properties, Santacruz must pay the Company an additional $0.3 million and $0.5 million in October 2017 and April 2018 respectively. Santacruz has the right to terminate the option agreement at any time, and the agreement will terminate if Santacruz fails to make a payment when due.