| PROPERTY, PLANT, EQUIPMENT, AND MINERAL PROPERTIES |
PROPERTY, PLANT, EQUIPMENT, AND MINERAL PROPERTIES Property, plant, equipment, and mineral properties were comprised of the following (in thousands): | | | | | | | | | | | | September 30, 2017 | | December 31, 2016 | Buildings and plant | | $ | 79,658 |
| | $ | 82,457 |
| Machinery and equipment | | 227,654 |
| | 227,987 |
| Vehicles | | 4,752 |
| | 4,750 |
| Office equipment and improvements | | 12,690 |
| | 12,505 |
| Ponds and land improvements | | 55,096 |
| | 57,474 |
| Total depreciable assets | | $ | 379,850 |
| | $ | 385,173 |
| Accumulated depreciation | | (135,491 | ) | | (116,194 | ) | Total depreciable assets, net | | $ | 244,359 |
| | $ | 268,979 |
| | | | | | Mineral properties and development costs | | $ | 138,882 |
| | $ | 138,578 |
| Accumulated depletion | | (25,410 | ) | | (21,974 | ) | Total depletable assets, net | | $ | 113,472 |
| | $ | 116,604 |
| | | | | | Land | | $ | 519 |
| | $ | 719 |
| Construction in progress | | $ | 4,937 |
| | $ | 2,188 |
| Total property, plant, equipment, and mineral properties, net | | $ | 363,287 |
| | $ | 388,490 |
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We incurred the following expenses for depreciation, depletion, and accretion, including expenses capitalized into inventory, for the following periods (in thousands): | | | | | | | | | | | | | | | | | | | | Three Months Ended September 30, | | Nine Months Ended September 30, | | | 2017 | | 2016 | | 2017 | | 2016 | Depreciation | | $ | 7,030 |
| | $ | 7,587 |
| | $ | 21,270 |
| | $ | 28,931 |
| Depletion | | 850 |
| | 727 |
| | 3,452 |
| | 2,708 |
| Accretion | | 390 |
| | 442 |
| | 1,168 |
| | 1,326 |
| Total incurred | | $ | 8,270 |
| | $ | 8,756 |
| | $ | 25,890 |
| | $ | 32,965 |
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