# Relationship history for MSHA mine 0900121

Current hierarchy: **Imerys S A → Kentucky-Tennessee Clay Company → Kentucky-Tennessee Clay Company**

- Valid-time bounds: inclusive, date granularity
- Null end: open-ended in the upstream history row; not independent proof of present control
- Transaction-time observation: 2026-10-18T09:31:49.615908+00:00

## Valid-time edges

- **operator_operates_mine:** Cyprus Industrial Minerals Company → Kentucky-Tennessee Clay Company; 1950-01-01 to 1980-09-21; source msha-controller-operator-history
- **controller_controls_mine:** Cyprus Mines Corp → Kentucky-Tennessee Clay Company; 1950-01-01 to 1980-09-21; source msha-controller-operator-history
- **controller_controls_operator:** Cyprus Mines Corp → Cyprus Industrial Minerals Company; 1950-01-01 to 1980-09-21; source msha-controller-operator-history
- **operator_operates_mine:** Cyprus Industrial Minerals Company → Kentucky-Tennessee Clay Company; 1980-09-22 to 1989-02-16; source msha-controller-operator-history
- **controller_controls_mine:** Cyprus Amax Minerals Company → Kentucky-Tennessee Clay Company; 1980-09-22 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Cyprus Amax Minerals Company → Cyprus Industrial Minerals Company; 1980-09-22 to 1989-02-16; source msha-controller-operator-history
- **controller_controls_mine:** Hecla Mining Company → Kentucky-Tennessee Clay Company; 1986-06-17 to current/open; source msha-controller-operator-history
- **operator_operates_mine:** Kentucky-Tennessee Clay Company → Kentucky-Tennessee Clay Company; 1989-02-17 to 2001-03-27; source msha-controller-operator-history
- **controller_controls_operator:** Hecla Mining Company → Kentucky-Tennessee Clay Company; 1989-02-17 to 2001-03-27; source msha-controller-operator-history
- **operator_operates_mine:** Kentucky-Tennessee Clay Company → Kentucky-Tennessee Clay Company; 2001-03-28 to current/open; source msha-controller-operator-history
- **controller_controls_mine:** Imerys S A → Kentucky-Tennessee Clay Company; 2001-03-28 to current/open; source msha-controller-operator-history
- **controller_controls_operator:** Imerys S A → Kentucky-Tennessee Clay Company; 2001-03-28 to current/open; source msha-controller-operator-history