The size of De Grey Mining's (ASX:DEG) already impressive Hemi gold discovery in the WA Pilbara looks certain to be lifted later this year as the company assesses and incorporates more good drilling data.

In a statement to the ASX on Monday, De Grey said it "is preparing an updated Hemi mineral resource estimate (MRE) incorporating these results," which is anticipated for release before the end of this year.

"The new extensional drill results in this release represent further potential upside to the definitive feasibility study (DFS) outcomes and support the Hemi underground mining concept," De Grey told the ASX.

One point to watch in the update is how the company changes its assumed gold price, which presently sits at A$2,700 an ounce—around A$1,000 under the world price (in Australian dollars) and looking to track higher if the Fed cuts rates in September. If the price moves, it could see a bigger rise in the project's MRE.

Monday's was the third statement in weeks from the gold explorer containing growing evidence that the Hemi's MRE is a lot bigger—with all the main areas now understood to be open at depth instead of being closed off in some areas. That suggests the prospects of a large underground mine are a stronger possibility down the track.

A statement in late June revealed good grades from extensional drilling around the Eagle deposit, and on July 11, De Grey released the results of a scoping study based on exploration results for smaller regional prospects around the core Hemi finds. The study was very positive, suggesting the smaller, regional discoveries could either boost annual production, extend the life of the mine, or improve the economics of an underground operation as well as the initial open cut.

In the July 11 ASX statement, De Grey said the Scoping Study presented "a strong financial and technical case for the potential development of the Hemi Regional deposits within the first five years of operations at Hemi and would be funded from operating cashflows from Hemi. The Regional Project development would not be funded by the Company's existing cash reserves."

Hemi currently comprises six main zones—Aquila, Brolga, Crow, Diucon, Eagle, and Falcon—but there are up to a dozen other areas of interest either associated with these main zones or in smaller pods or areas of mineralization.

The main Hemi zones have a current mineral estimate of 10.5 million ounces of gold and the potential to be mined by large-scale, low strip ratio, low-cost open pit mining, but with the growing possibility for an underground operation as the mining of the existing areas matures.

The total resource at Hemi and its smaller deposits and areas of mineralization is currently estimated to be 12.7 million ounces of gold. The three statements, capped by Monday's release, suggest very strongly that both the Hemi resource figure and the overall figure will be lifted later this year.

The late June statement included details of extended mineralization at the Eagle deposit for a further 200 meters down plunge, with mineralization still open at depth and potentially along strike.

De Grey said on Monday that drilling at the Aquila and Crow deposits in the northern region of the Hemi project has the potential to further add to the Hemi mineral resource estimate (MRE) and bolster the production profile set out in the company's definitive feasibility study (DFS).

The Aquila-Crow intrusive body currently extends up to 1km east-west and 0.7km north-south. The intrusive body was originally interpreted to pinch out at depth below Aquila. More recent interpretation suggests the mineralization continues at depth.

The company said diamond and reverse circulation ("RC") drilling are ongoing at Aquila, Falcon, and Antwerp and planned for Scooby (a smaller regional area), "seeking to further add to the MRE and provide potential upside to the Hemi Definitive Feasibility Study2 ("DFS") production profile."

As well, discovery and MRE extension drilling is continuing within the Greater Hemi area and regional targets including West Yule and the Egina Joint Venture.

"Drilling beneath the DFS pit shells and below the current mineral resource at Aquila-Crow demonstrates that a large mineralized system extends to depth and is still open," De Grey general manager exploration Phil Tornatora told the ASX on Monday.

The nearby McLeod lodes are high-grade lodes occurring in the south-east of the Crow deposit. The lodes show different characteristics to the bulk of the Hemi mineralization and are generally associated with a smokey quartz veining with visible gold.

"The McLeod lodes in the south of Crow continue to return high-grade intercepts and it is exciting to see similar style mineralization persists in deeper holes below Aquila," Tornatora said. "This extension drilling has strong potential to add to the Hemi MRE, in addition to supporting conceptual studies into potential future underground mining."

De Grey announced earlier this month that it had locked in more than A$1 billion from banks and government agencies to finance the development at Hemi, as well as having around A$800 million in the bank to finance exploration and pre-mine orders.