The Empire State Mine is located in New York, US. (Credit: James St. John/Wikipedia)
Location map of the Empire State Mine. (Credit: Titan Mining Corporation)
A sample of zinc ore. (Credit: James St. John/Flickr)

The Empire State Mine (ESM) project comprises a group of high-grade zinc mines in the US state of New York.

The group includes an operational mine (ESM 4) and six historic mines- ESM 1, 2 and 3, Hyatt, Pierrepont and Edwards.

The project is fully owned by Titan Mining Corporation.

In September 2017, a Preliminary Economic Assessment (PEA) for ESM was completed. It was followed by an updated mineral resource at ESM 4 in April 2018. Titan Mining commissioned the mill and announced the start of ore recovery in January 2018.

An amended technical report for the mining operation was published in February 2021.

Empire State Mine Location

The Empire State Mine is located 7miles from the Gouverneur Town in New York, the US, around 1.3-miles south-west of Fowler, in St. Lawrence County.

Overall, Titan owns 2,699 acres of fee simple surface and mineral rights in three towns in St. Lawrence County.

The ESM, mill and tailings disposal facility are located in a 1,754-acre area in the town of Fowler. Nine parcels of land totalling 703 acres in the town of Edwards feature the Edwards mine, while the remaining fee ownership includes the Pierrepont mine.

The site can be accessed by State Road 812 from the St. Lawrence Seaway, Ogdensburg, New York.

Ownership and Operational History

The Balmat-Edwards district has four mines.

St. Joe Minerals & predecessors mined Edwards in 1915 and Balmat in 1930. The company held ownership of the mine from 1915 to 1987.

Zinc Corporation of America (ZCA) became the owner of the operation in 1987 and mined it through 2001.

OntZinc, later renamed as Hudbay Minerals, purchased ZCA and carried out mining operations from 2005 to 2008.

Star Mountain Resources purchased SLZ (a subsidiary of Titan Mining Corporation) from Hudbay in 2015 and got ownership till 2016.

In December 2016, Titan US purchased Balmat Holding’s shares, which itself had the shares of SLZ. Subsequently, the Balmat mine was renamed as Empire State Mines by Titan.

The Balmat mine operated continuously from 1930 to 2001, and from 2006 to the third quarter of 2008, when the mine was put on care and maintenance due to fall in metal prices.

Operations at ESM4 recommenced in 2018.

Historically, the mine has produced a total of 33.8 million tonnes (Mt) grading 8.6% zinc.

Empire State Mine Geology and Mineralisation

Predominantly, the main structure at the site is a major south-west to north-east trending fold called Sylvia Lake Syncline between the original Balmat mine and the Edwards mine.

The Upper Marble Formation is extensively deformed and has limited aerial exposure.

The property’s mineralisation is categorised as sedimentary exhalative (Sedex) in origin consisting of primarily massive sphalerite with minor pyrite and galena.

Sphalerite-bearing deposits are found in siliceous dolomitic and evaporite-bearing marbles of the Upper Marble Formation of the Balmat-Edwards marble belt. These zinc-sulphide deposits occur in the core of the Sylvia Lake Syncline.

There are 14 known zones of sphalerite mineralisation in the property.

Mineral Resource Estimate

As of October 2020, the underground (measured and indicated) mineral resource estimate for ESM is 1.71 million US short tonnes containing 401.9Mlbs zinc at a grading of 11.72%.

The inferred mineral resources for the project are 6.55 million US short tonnes containing 1,455.6Mlbs zinc at a grading of 11.11%.

Open pit resource estimate is 701,000 US short tonnes in measured and indicated categories containing 43.8Mlbs at 3.13% Zn. Inferred resource estimate stands at 217,000 US short tonnes containing 14.6Mlbs at 3.37% Zn.

Mining and Ore Processing

At Empire State Mine, the ore is extracted by using Longitudinal Retreat Stoping (LRS), Cut and Fill (C&F), Panel Mining- Primary and Secondary (PAP & PAS), Development Drifting underground mining methods with rock backfill, and Long Hole Backstopes (BCK) methods.

The combination of underground and open pit mining was expected to achieve production rate of 1,200t/d in 2021 and 1,800t/d in 2022.

The mine will have a life of seven years, with open pit mining expected to be completed in year three (2024).

The mined mineral is processed at the existing ESM concentrator, commissioned in 1970, with a design capacity of 5,000t/d.

The flowsheet includes crushing, grinding, sequential lead and zinc flotation circuits, concentrate dewatering circuits, and loadout facilities.

After being crushed and grinded, the ore enters zinc flotation circuit which consists of rougher flotation.

The roughed output is transferred to scavenger flotation from where, the scavenger concentrate enters the head of the rougher circuit.

The rougher concentrate enters cleaner flotation where it undergoes two stages of cleaning. Subsequently, cleaner tailings go back to the previous flotation stage and the cleaned concentrate undergoes dewatering in concentrate dewatering circuits.

Presently, zinc concentrate is being produced at an average of 59% zinc, 3% iron, and 0.50% magnesium. Lead is present in minute quantity, so no lead concentrate is planned to be produced.

Contracts and Offtake Agreement

The technical report of the Empire State Mine, published in 2021, was prepared by AMC Mining Consultants (Canada).

Underground mining contractor Dumas was associated with this zinc project.

Cabo conducted underground drilling from 2018 to 2019, while Boart Longyear was engaged for all surface programmes from 2018 to 2020.

In February 2018, an offtake agreement was signed by Titan with Glencore for 100% zinc concentrate from the mine. The contract commenced with the first production of concentrate.