A review draft profile of the 2018 Taylor Deposit preliminary economic assessment, describing the proposed 10,000 st/d (9,072 t/d) crushing, SAG/ball mill grinding, differential lead-zinc flotation, and dry-stack tailings process route.
Report context
The report was prepared by AMC Mining Consultants (Canada) Ltd. for Arizona Mining Inc., covering the Taylor Zn-Pb-Ag deposit on the Hermosa Property in Santa Cruz County, Arizona. The processing section describes a proposed design for a new 10,000 short tons per day (stpd) facility, not an existing operation. All figures and descriptions below represent design criteria and flowsheet intent from that 2018 study.1–17.12.2.2 (Recovery methods).
Processing route
The proposed Taylor processing facility is designed to treat 10,000 stpd (9,072 tonnes per day) of run-of-mine (ROM) material through a conventional crushing, grinding, and differential flotation circuit. The design separates lead and zinc minerals into separate concentrates, with final tailings dewatered to a dry-stack disposal area. The flowsheet includes an integral regrind circuit for lead and zinc rougher concentrates, and a comprehensive water management system that recycles process water.
Primary crushing and coarse stockpile
ROM material is delivered to the crushing plant by rear-dump trucks and dumped into a dump hopper using a front-end loader. A grizzly screen removes oversize, which feeds a primary jaw crusher. Two mobile rock breakers service the crusher/screen and the ROM area stockpile. The crusher reduces material from a maximum feed size of 19.7 in (500 mm) to approximately P100 of 9.6 in (243 mm). Crushed material is conveyed to a ground stockpile with a live storage capacity of approximately 10,000 tons (9,072 tonnes). A reclaim tunnel beneath the stockpile uses variable-speed belt feeders to transfer material to the SAG mill feed conveyor. Dust control includes water sprays at the dump pocket, dust collector vents at transfer points, and a wet-type dust collection system on the stockpile feed and reclaim tunnel.
Grinding circuit
The grinding circuit consists of a semi-autogenous (SAG) mill operating in closed circuit with a vibrating screen, followed by a ball mill in closed circuit with hydrocyclones. The SAG mill discharge is screened at 10.0 mm bottom openings; screen oversize is recirculated to the SAG mill feed, while undersize reports to the cyclone feed pump box. The target SAG grind is P80 of 2,191 microns. The ball mill discharge combines with vibrating screen undersize in the cyclone feed pump box, pumped by variable-speed horizontal centrifugal slurry pumps (one operating, one standby) to a hydrocyclone cluster. The hydrocyclone overflow, at 80% passing 150 microns, flows by gravity to a tramp oversize screen before flotation. Zinc sulfate (ZnSO4) and sodium cyanide (NaCN) are added into the ball mill for process control.
Lead flotation and regrind
The lead flotation circuit comprises one row of eight tank-type rougher cells, each 1,766 ft³ (50 m³), with a regrind circuit. Lead rougher concentrate is pumped to a regrind cyclone feed pump box and combined with regrind mill discharge. The regrind cyclone cluster operates in closed circuit with a lead regrind mill; overflow (the final regrind product) is sampled for particle size and analysed by on-stream analysers before flowing to a lead cleaner conditioning tank. The lead cleaner circuit consists of eleven cells: two first cleaner cells (300 ft³ / 8.5 m³), four first cleaner scavenger cells (300 ft³ / 8.5 m³), three second cleaner cells (100 ft³ / 2.8 m³), and two third cleaner cells (100 ft³ / 2.8 m³). Lead third cleaner concentrate flows by gravity to the lead concentrate thickener. Lead rougher tailing and first cleaner scavenger tailing flow by gravity to the zinc rougher conditioning tank.
Zinc flotation and regrind
Lead rougher tailing and lead first cleaner scavenger tailing flow by gravity to a zinc rougher conditioning tank. The zinc rougher circuit consists of eight tank-type cells (1,766 ft³ / 50 m³). Zinc rougher concentrate is pumped to a regrind mill, with the regrind product feeding a cyclone cluster. The zinc cleaner circuit comprises fifteen cells: four first cleaner cells (300 ft³ / 8.5 m³), eight first cleaner scavenger cells (300 ft³ / 8.5 m³), and three second cleaner cells (100 ft³ / 2.8 m³). Zinc second cleaner concentrate is pumped to the zinc concentrate thickener. Zinc rougher tailing reports by gravity to a tailing sample box, then to the tailing thickener.
Concentrate dewatering
Lead third cleaner concentrate is pumped to a lead concentrate thickener. The thickener underflow is pumped (one operating pump, one spare) to an agitated storage tank, then to a pressure filter. Filter cake discharges to a covered lead concentrate stockpile. Zinc second cleaner concentrate is thickened, with underflow pumped to an agitated tank and then to a pressure filter; filter cake discharges to a covered zinc concentrate stockpile. Both concentrates are reclaimed by front-end loader onto highway haulage trucks, with a truck scale located near the load-out area.
Tailing dewatering and disposal
Zinc rougher flotation tailing flows by gravity to a high-rate tailings thickener. Thickener overflow is returned to the process water tank. Thickener underflow is pumped by variable-speed horizontal centrifugal slurry pumps (one operating, one standby) to a tailing filter feed tank, then to five filters (four operating, one standby). Filter cake discharges to conveyors. Sixty percent (60%) of the final filtered tailing is transferred to the backfill plant; the remainder is placed via a mobile/stacking conveyor system to build a dry-stack tailings storage facility (TSF). Damp tailings are delivered by conveyors and placed behind a tailings buttress using a radial stacker; a dozer spreads and compacts the material for trafficability. Dry disposal eliminates the need for an engineered embankment and seepage containment system, conserves water, and minimizes site disturbance.
Reagents and water systems
Reagents requiring receiving, handling, mixing, and distribution systems include: zinc sulfate (ZnSO4·7H2O), Aerofloat 242 (promoter), carboxymethyl cellulose (CMC), copper sulfate (CuSO4·5H2O), sodium isopropyl xanthate (SIPX), methyl isobutyl carbinol (MIBC, frother), sodium cyanide (NaCN), and flocculant.
Fresh water is supplied from property wells to a fresh water tank (also used for fire suppression). The fresh water system supplies process makeup, reagent mixing, and gland water. Process water is split into lead and zinc circuits: the lead process water tank receives overflow from the lead concentrate thickener and tailings thickener, and is used as makeup in the primary cyclone feed sump; the zinc process water tank receives overflow from the zinc concentrate thickener and excess lead process water, used as makeup in the zinc flotation circuit.
Key reported parameters
| Parameter | Value / Description | Unit / Basis |
|---|---|---|
| Plant throughput | 10,000 stpd (9,072 t/d) | Design capacity, nominal |
| ROM feed size | Max 19.7 in (500 mm) to P100 9.6 in (243 mm) | Design crushing duty, primary jaw crusher |
| SAG mill product | P80 2,191 microns | Design target, SAG mill discharge |
| Final grind (cyclone overflow) | 80% passing 150 microns | Design target, grinding circuit product |
| Lead regrind circuit | Regrind mill + hydrocyclone cluster | Design, closed circuit |
| Zinc regrind circuit | Regrind mill + hydrocyclone cluster | Design, closed circuit |
| Lead flotation cells | 8 rougher (1,766 ft³/50 m³), 2+4+3+2 cleaners | Design, tank-type forced air |
| Zinc flotation cells | 8 rougher (1,766 ft³/50 m³), 4+8+3 cleaners | Design, tank-type forced air |
| Lead concentrate dewatering | Thickener + pressure filter | Design, covered stockpile |
| Zinc concentrate dewatering | Thickener + pressure filter | Design, covered stockpile |
| Tailings filtration | 5 filters (4 operating, 1 standby) | Design, high-rate thickener feed |
| Filtered tailings split | 60% to backfill, 40% to dry-stack TSF | Design, after filtration |
| Water sources | Property wells; process water tanks (lead, zinc) | Design, fresh water makeup to each circuit |
Project website: https://portergeo.com.au/database/mineinfo.php?mineid=mn1685
Technical qualifications
All process descriptions and parameters represent proposed design criteria from that study, not installed or operating performance. The report's effective date is 1 January 2018, and the study was submitted on 16 January 2018; it does not show any subsequent changes to ownership, project status, or design. The original report includes a figure (Figure 17.1) referenced but not reproduced in the Markdown; therefore, the flowsheet is described textually here. The report's Section 17 omits details on lead regrind mill specifications (Section 17.4 is not present in the supplied text), and Section 17.8 (zinc concentrate dewatering) is partially described. No data were supplied on metallurgical testwork, recovery estimates, or actual operating results; all recovery claims in the original study are not present in the cited sections, and none are inferred here. The original report's qualitative statements (e.g., "dry tailings disposal results in a very compact site") are quoted directionally from the source; they are not engineering performance guarantees.
Source: AMC Mining Consultants (Canada) Ltd., "Hermosa Property Mineral Resource and Taylor Deposit PEA update," for Arizona Mining Inc., effective date 1 January 2018, submitted 16 January 2018, Sections 17.1–17.3, 17.5–17.6, 17.8–17.9, 17.10, 17.11, 17.12.2.
