4. PROPERTY, PLANT AND EQUIPMENT, NET (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Mineral rights	$ 2,724,154	$ 2,764,462
Buildings	59,007,466	59,880,567
Plant and machinery	231,247,364	234,669,007
Motor vehicles	6,039	6,129
Furniture, fixtures and office equipment	3,188,556	3,235,736
Construction in progress	5,562,402	1,204,742
Total	301,735,981	301,760,643
Less: accumulated depreciation and amortization	(151,706,607)	(146,330,705)
Impairment	(17,180,774)	(17,434,989)
Net book value	$ 132,848,600	$ 137,994,949