ACQUISITIONS (Details) $ in Thousands, oz in Millions								1 Months Ended		12 Months Ended
	Jul. 05, 2020 USD ($)	Apr. 03, 2020 USD ($)	Mar. 30, 2020 USD ($)	Feb. 02, 2020 USD ($)	Jan. 29, 2020 USD ($)	Nov. 05, 2019 USD ($)	Feb. 25, 2019 USD ($) oz t	Nov. 30, 2019 USD ($)	Aug. 31, 2019 USD ($) payment	Jun. 30, 2020 USD ($) shares	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2020 $ / shares
Acquisitions
Acquisition consideration paid										$ 155,985	$ 1,055	$ 11,812
Investment value										$ 17,900	$ 16,000
Throughput levels | t							13,000
TriStar
Acquisitions
Common stock that can be purchased by warrants (in shares) | shares										19,640,000
Contango
Acquisitions
Investment shares owned (in shares) | shares										809,744
Alturas
Acquisitions
Acquisition consideration paid					$ 11,000
Future payment based on project decisions					20,000
Alturas | Maximum
Acquisitions
Acquisition consideration					41,000
Future payment to private individuals upon first production					$ 10,000
Alturas | Gold
Acquisitions
Net smelter return (NSR) (as a percent)					1.06%
Alturas | Copper
Acquisitions
Net smelter return (NSR) (as a percent)					1.59%
CDS
Acquisitions
Net smelter return (NSR) (as a percent)									1.50%
Acquisition consideration									$ 7,500
Acquisition consideration paid			$ 1,500					$ 1,500	$ 4,500
Number of installments | payment									3
CDS | TriStar
Acquisitions
Common stock that can be purchased by warrants (in shares) | shares										19,640,000
Investment value										$ 4,000
Exercise price of warrants | $ / shares													$ 0.25
Term of warrants										5 years
Khoemacau
Acquisitions
Acquisition consideration	$ 146,800
Acquisition consideration paid	$ 11,100	$ 47,900		$ 22,000		$ 65,800
Silver production acquired (as a percent)							80.00%
Option contribution amount							$ 53,000
Silver production option (as a percent)							20.00%
Rate reduction (as a percent)							50.00%
Silver production after threshold (as a percent)							40.00%
Rate reduction threshold | oz							32
Rate reduction threshold with option | oz							40
Spot price paid (as a percent)							20.00%
Increased level of throughput (as a percent)							30.00%
Loan receivable commitment							$ 25,000
Loan receivable term							7 years
Khoemacau | LIBOR
Acquisitions
Loans receivable variable interest rate (as a percent)							11.00%