| 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): | | | | | | | | | | | | March 31, 2017 | | December 31, 2016 | Buildings and plant | | $ | 79,432 |
| | $ | 82,457 |
| Machinery and equipment | | 225,570 |
| | 227,987 |
| Vehicles | | 4,743 |
| | 4,750 |
| Office equipment and improvements | | 12,598 |
| | 12,505 |
| Ponds and land improvements | | 54,990 |
| | 57,474 |
| Total depreciable assets | | $ | 377,333 |
| | $ | 385,173 |
| Accumulated depreciation | | (121,559 | ) | | (116,194 | ) | Total depreciable assets, net | | $ | 255,774 |
| | $ | 268,979 |
| | | | | | Mineral properties and development costs | | $ | 138,785 |
| | $ | 138,578 |
| Accumulated depletion | | (23,742 | ) | | (21,974 | ) | Total depletable assets, net | | $ | 115,043 |
| | $ | 116,604 |
| | | | | | Land | | $ | 519 |
| | $ | 719 |
| Construction in progress | | $ | 2,957 |
| | $ | 2,188 |
| Total property, plant, equipment, and mineral properties, net | | $ | 374,293 |
| | $ | 388,490 |
|
We incurred the following expenses for depreciation, depletion, and accretion, including expenses capitalized into inventory, for the following periods (in thousands): | | | | | | | | | | | | Three Months Ended March 31, | | | 2017 | | 2016 | Depreciation | | $ | 7,160 |
| | $ | 12,482 |
| Depletion | | 1,774 |
| | 1,444 |
| Accretion | | 389 |
| | 442 |
| Total incurred | | $ | 9,323 |
| | $ | 14,368 |
|
|