The company said it had completed the first blast on the Mad Kiss portal late last week.
It expects to award the underground development contract this quarter, which should provide access to principal underground mining areas including some higher-grade zones at Mad Kiss and East Walcott that could potentially provide supplemental mill feed during development.
"The decline provides an ideal platform to potentially upgrade and expand the current underground resource and unlock the full potential of the Aurora deposit," president and CEO Scott Caldwell said.
Last month, Caldwell had offered reassurance of a strong fourth quarter but within weeks had to lower production guidance for the second time this year, citing grade variability at the Guyana mine.
The company's original 2018 guidance of 190,000-210,000oz had been reduced in July to 175,000-185,000oz, and was further reduced last month to 150,000-155,000oz.
Cost guidance was increased again to US$1,025-$1,050/oz.
The company has initiated a review of the underlying resource model and is also anticipating a revision of the life-of-mine production profile.
Guyana Goldfields expects its contractor to complete and reinforce the collar at Mad Kiss and extend the decline 200m early in the first quarter of 2019 to complete the early works phase.
Shares in the company, which were trading above C$3 two weeks ago before virtually halving in value on the latest guidance cut, fell 3.61% on Friday to C$1.60 to capitalise it over $277 million.