The total resource is now estimated at 38.48 million tonnes down to the 920 metre level.
That's 16% more than the 33.12 million tonnes estimated in March 2012 but that was only down to 855metres.
Notably, the resource remains open at depth.
Estimated grades have now been based on the production plant using a 1.25mm screen (to sift material), compared to 1.00 mm screens previously.
This does mean that grade will be significantly lower, but the carat value will be higher as the smallest diamonds no longer being recovered also have the lowest value.
The recoverable diamonds from this resource at the increased bottom screen size of 1.25 mm is estimated at 9.39 million carats, compared to 13.39 million carats, at 1.00 mm screen size.
Within the overall resource, 2.21 million tonnes of the UK4 Block has been classified as a reserve between the 230 and 370m levels.
This whole block could be mined for 60 months at a rate of 35,000 tonnes per month and generate a positive NPV of R133.3 million (US$8.9 million) and a robust IRR of 59%, the miner said.
DiamondCorp plans to mine the high-grade K4 kimberlite within this reserve first while the first block cave is established on the 500m level (being outside of the current mineral reserve estimate).
"There may well be opportunities to optimize the mine plan as more K4 is found to be present as the mine progresses. When block caving progresses, any unmined portions of this reserve would then be extracted in subsequent caves," it added.
The mine is now in operation and full production rates of 30,000 tonnes per month throughput are likely to be reached in July of this year, the firm has said previously.
Broker Panmure repeated a 'buy' on the stock and targets 15.7p.
"The report, we believe, provides reassurance to investors ahead of commercial production being announced in 2016," said analyst Kieron Hodgson.
"With a notable improvement in valuation offsetting the well flagged grade reduction, associated with the bottom cut off change to 1.25mm, we believe future sales updates can provide a catalyst for further gains."
The broker now models ROM (run-of-mine) production at $164/ct compared to $135/ct and ascribes no value for any high value special goods such as the 22ct high-quality diamond, recently placed into partnership, and the coloured goods Lace is known to produce.
Hodgson also highlights that market demand continues to show signs of improvement and is being supported by restocking efforts following the recent end of year retail period.
DiamondCorp shares eased 1.43% to 8.625p.