Upgrades boost Hope Bay gold recoveries
North of 60 Mining News – June 22, 2018
Last updated 9/25/2020 at 5:32am
TMAC Resources Inc. June 14 reported that the addition of a Falcon gravity concentrator to the recovery circuit processing ore from the Doris Mine at the company's Hope Bay project has resulted in record monthly gold production at the Nunavut operation.
The mill at Hope Bay reached commercial production last May, but poor gold recoveries has hampered the ability to reach full operating capacity.
"TMAC's recent metallurgical tests have indicated that at least 70 percent of the Doris mine contained gold can be recovered by gravity processes, but throughout 2017 only around 20 percent of the gold was recovered by gravity, which put severe gold overloading and stress on both the flotation and concentrate treatment plant circuits," said TMAC COO Gil Lawson.
The company began making improvements last year by installing a dewatering cone, which helped the plant achieve 76 percent recoveries from all circuits, a marked improvement over the 67 percent average recoveries previously achieved.
This installation of the first of two Falcon SB400 gravity concentrators is further boosting gold recoveries. As a result, gold recovery increased to 83 percent in May, an improvement from 76 percent in April and 71 percent in the first quarter.
During May, the mill at Hope Bay produced 9,850 ounces of gold from 28,900 metric tons of ore averaging 12.7 grams per ton gold. This is a 28 percent improvement over the previous best month of November, despite the 22 percent higher ore grades in November.
This improvement is to the north circuit line, one of two 1,000 metric ton per day recovery circuits to be operated at Doris Mine. Commissioning of the south circuit line has been postponed until improvements were implemented to the twin north line.
TMAC installed and wet commissioned the south line by the end of May and rock commissioning began on June 3. The south line includes the upgrades made to north line, including its own Falcon concentrator.
The next critical step is the integration of the two concentrator lines into the concentrate treatment process to achieve overall plant capacity of 2,000 metric tons per day.
"We commenced feeding low-grade ore to CL2 (south line) in early June and it is ramping up to deliver overall plant capacity of 2,000 tonnes (metric tons) per day," said Lawson. "The mine continues to ramp up production to feed the growing Plant capacity. With increased throughput, grade and recoveries we expect to drive our all in sustaining costs significantly lower as fixed costs are spread over increasing gold production."
Further improvements to both lines are expected later this year.
"We have ordered additional gravity concentrator units that will be installed beginning later this summer that will drive further improvements and take us to the point where we will begin optimization and seek our ultimate recovery target of greater than 90 percent," the TMAC COO said.
Value with the drill-bit
As mill upgrades improve recoveries, drilling continues to extend the zones of high-grade gold at Doris and across the wider Hope Bay property.
TMAC CEO Jason Neal said the high-grade gold tapped so far this year at Doris North Below the Dyke, referred to as Doris North BTD, and at Madrid North areas of Hope Bay demonstrate "TMAC's great potential to grow value with the drill-bit."
Discovered in 2016, the Doris BTD zone lies below a roughly 100-meter thick layer of diabase, dark-colored igneous rock, that underlies the Doris North deposit.
Doris North BTD has proven to be a significant expansion of high-grade gold at Hope Bay and TMAC has extended underground working from Doris North into BTD.
This year's underground drilling into a zone known at BTD Extension has cut the highest grade gold TMAC has ever encountered in drilling at Hope Bay.
This hole, TM500148, cut 0.66 meters averaging 2,710 g/t (87.13 oz/t) gold, part of a 7.1-meter intercept averaging 261.4 g/t (8.4 oz/t) gold.
Doris North BTD Extension, interpreted as the down-dropped continuation of the Doris North Hinge structure on the north side of a fault, is the highest grade area identified so far at Doris.
TM500152, also drilled at BTD Extension, cut 1.5 meters averaging 1,255 g/t (40.35 oz/t) gold.
"Drilling on the Doris North BTD zones has demonstrated that the high grade, Doris North Hinge structure continues to the north, below the diabase dyke, and has the potential to add significant high-margin gold ounces to the Doris mineral resources inventory," said Neal.
The company also reported encouraging results from surface drilling at Madrid North, a deposit about eight kilometers (five miles) south of Doris.
The Madrid North deposit consists of four separate mineralized zones – Naartok West, Naartok East, Rand and Suluk.
"The Madrid North surface drilling program is focused on the Naartok West zone, and has confirmed the continuity of the thick, high grade core of the mineralized zone near surface, which will assist in the detailed planning of the Madrid North advanced exploration and bulk sampling program scheduled to commence in 2019," explained the TMAC CEO.
Highlights from the 2018 drilling at Naartok West include 25.1 meters averaging 11.5 g/t gold in hole TM00375; and 50 meters of 12.9 g/t gold in hole TM00376.
So far, nine holes have been drilled at Madrid North and TMAC said drilling is continuing there into the second half of the year.