MINING PROPERTIES

Mining properties consist of the following (in thousands):



September 30, 2018	Palmarejo			Rochester			Silvertip			Kensington			Wharf			La Preciosa		Other			Total
Mine development	$	233,562		$	196,143		$	105,320		$	322,901		$	41,498		$	—	$	—		$	899,424
Accumulated amortization	(159,120		)	(149,729		)	(389		)	(191,026		)	(17,811		)	—		—			(518,075		)
	74,442			46,414			104,931			131,875			23,687			—		—			381,349
Mineral interests	629,303			—			245,116			—			45,837			49,085		5,171			974,512
Accumulated amortization	(463,565		)	—			(988		)	—			(25,843		)	—		(422		)	(490,818		)
	165,738			—			244,128			—			19,994			49,085		4,749			483,694
Mining properties, net	$	240,180		$	46,414		$	349,059		$	131,875		$	43,681		$	49,085	$	4,749		$	865,043



December 31, 2017	Palmarejo			Rochester			Silvertip		Kensington			Wharf			La Preciosa		Total
Mine development	$	214,383		$	193,881		$	57,214	$	298,749		$	40,618		$	—	$	804,845
Accumulated amortization	(146,598		)	(144,390		)	—		(178,632		)	(15,748		)	—		(485,368		)
	67,785			49,491			57,214		120,117			24,870			—		319,477
Mineral interests	629,303			—			245,116		—			45,837			49,085		969,341
Accumulated amortization	(435,215		)	—			—		—			(24,034		)	—		(459,249		)
	194,088			—			245,116		—			21,803			49,085		510,092
Mining properties, net	$	261,873		$	49,491		$	302,330	$	120,117		$	46,673		$	49,085	$	829,569

In February 2018, the Company completed the sale of the Manquiri Divestiture. Pursuant to the terms of the agreement, the Company received, among other consideration, the NSR. Coeur estimates the value of this net smelter returns royalty to be approximately $7.1 million, which is included in Other. In September 2018, the Company entered into the Letter Agreement, pursuant to which the Company agreed to suspend the quarterly payments in respect of the NSR until October 15, 2019. Based on the Company’s evaluation of the terms of the Letter Agreement, the Company recorded a write-down of $1.9 million on the NSR. See Note 10 -- Fair Value Measurements and 21 -- Discontinued Operations for additional detail.

The Silvertip mine reached commercial production on September 1, 2018. The determination of commercial production (or ready for intended use) was based on many factors requiring the exercise of judgment. Factors that were considered when determining if intended use had been achieved included achievement of continuous production or other output, mineral recoveries at or near expected levels, the absence of routine take-downs of the plant to address commissioning issues and fix problems, and the release of the commissioning team.

Prior to commercial production, costs related to mine development, construction of long-lived assets, and inventory were capitalized; all other costs were expensed in the period incurred. Amortization of mining properties commenced when the mine reached commercial production.