Underground Mining

Rory's Knoll
The Optimized LOM plan demonstrates improved economics through accelerating selective underground mining of higher grade stopes concurrent with open pit operations. Following a two-year pre-production period, underground mining at Rory's Knoll is expected to be fully ramped up in year 2022. Long hole open stoping ("LHOS") will initially target higher grade material between the bottom of the pit from -240 metres below river level ("mRL") and -460 mRL. In 2023, the Crown Pillar will be blasted and mining will then transition to sublevel cave mining (SLC) for the remainder of the mine life at an estimated average mining rate of 4,700 tpd. An improved mine schedule is expected to provide supplemental feed from the other satellite deposits later in the mine life which resulted in Rory's Knoll underground mining becoming deeper by approximately 200 metres than what the previous 2017 Feasibility Study envisioned.

Accelerating underground development is also expected to provide an ideal platform to potentially upgrade and expand the underground resource, especially at East Walcott where limited historical drilling has produced exceptional results. Initial underground mine development will be conducted primarily by contract underground mining experts. An extensive training and development program will allow the transition to an underground workforce that is expected to be composed of approximately 80% Guyanese Nationals over the life of the underground operations.

Satellite Deposits – Mad Kiss & Aleck Hill
The Mad Kiss underground contributes an estimated 107,00 ounces (0.6 Mt at an average grade of 5.18g/t Au) to the overall Optimized LOM Plan. Mad Kiss is expected to be developed concurrently with the Rory's Knoll underground with initial production expected in 2019 and continuing through to 2021. Mad Kiss will be mined via longitudinal LHOS from a depth of about -10 mRL to about -400 mRL.

The Aleck Hill underground is expected to contribute 153,000 ounces (1.1 Mt at an average grade of 4.28 g/t Au) to the overall Optimized LOM Plan beginning in 2028 and continuing through to 2033. Aleck Hill will be mined through a combination of transverse and LHOS from a depth of about -140 mRL to about -500 mRL.

Processing

The existing process circuit has a capacity for 5,600 tpd and includes a cyanide leach and carbon adsorption process comprising crushing, single-stage grinding, gravity, cyanide leaching, carbon adsorption, carbon elution and regeneration, gold refining, cyanide destruction and tailings disposal.

The proposed plant expansion to 7,500 tpd will be completed in two phases. The first phase is currently ongoing and is expected to be completed by the end of the first quarter of 2018. This expansion is expected to increase the hard rock throughput rate from 5,600 tpd to 6,600 tpd and consists of debottlenecking the back end of the circuit and includes the addition of three leach tanks, a pre-leach thickener, carbon management systems and the expansion of the elution circuit. Due to additional retention time within the leaching circuit, the phase one mill expansion is expected to increase recoveries by approximately 1% to an estimated average recovery of 92.5%.

The second phase of the expansion will allow the continued processing of 7,500 tpd of hard rock ore and is expected to be completed by the end of the fourth quarter of 2018. It includes the utilization of a pre-crushing circuit and ball mill from a previously purchased 1,000 tpd modular processing plant. Results from a series of bulk test work on expanding the pre-crushing capacity have been highly encouraging demonstrating an approximate 3% improvement in grind as well as an approximate 2% overall improvement in gold recovery. Once completed, the overall gold recovery is expected to significantly increase to approximately 95.0%. In addition, a significant increase in gravity recoveries results in lower overall reagent consumption. The Company has awarded JDS Mining with the engineering and procurement for the Phase 2 Mill Expansion.

Financials

Operating cash costs¹ (including the royalty expense) average US$627 per ounce over the LOM. AISC¹ over the life of the mine, assuming an annual corporate general and administrative ("G&A") expense and stock based compensation of US$8 M and annual exploration expenses of US$5 M, are expected to average US$797 per ounce over the LOM.  A summary of the annual costs plan is included at the end of this press release and highlights are provided below.

Gold Price Sensitivity

Aurora Gold Mine Mineral Reserves

The Company has updated its mineral reserves for its Aurora Gold Mine utilizing a gold price of US$1,200 per ounce and has an effective date of December 31, 2017. Overall mineral reserves increased by 12% to 4.0 Moz compared to the most recent mineral reserve estimate which had an effective date of December 31, 2016 and also utilized a gold price of US$1,200 per ounce.

Aurora Gold Mine Mineral Resources

2018 Guidance

The Company's production and cost guidance for 2018 is provided below. Production is expected to be weighted towards the second half of the year due to mine sequencing and increased throughput to be available with the completion of the phase 1 expansion after the first quarter of 2018.  The 2018 mine plan is primarily made up of all hard rock ore from the central tonalite/diorite ore at Rory's Knoll and East Walcott deposits.

Cost of sales are expected to be US$850-$900 per ounce and AISC¹ of US$830-$880 per ounce.  These costs are based on an increased stripping rate during 2018, offset by the increased and more cost-efficient production offered by the process plant expansion investments. The royalty cost is based on an assumed gold price of US$1,200 per ounce. 

Conference Call

The Company will hold a conference call on Wednesday, February 21, 2018 at 10:00am EST where senior management will discuss the key findings of the Optimized LOM Plan and respond to any questions.

A webcast will be available on the Company's website following the call or through the following link at:
http://event.on24.com/r.htm?e=1599688&s=1&k=FD85236DBA07FD4CFDEF52E370E1C980

To join the call:

Conference Call Details:
Date of Call: Wednesday, February 21, 2018
Time of Call: 10:00am EST
Conference ID: 5267697

Dial-In Numbers:
North America Toll-Free: (888) 231-8191
International: (647) 427-7450

A recorded playback of the call will be available until February 27, 2018 by dialing: 1-855-859-2056 or 416-849-0833 and entering the call back passcode 5267697.

Workshop Presentation

The Company will host a teach-in technical workshop for analysts and institutional investors on Wednesday, February 21, 2018 starting at 11:00AM EST in Toronto at Vantage Venues (Formerly St. Andrew's Conference Centre) to discuss the results of the Optimized LOM Plan. The event will be webcast and the accompanying presentation will be available on the Company's website under the Investors and Events & Presentations section at www.guygold.com.

For further details on this event or to rsvp, contact Jacqueline Wagenaar, VP Investor Relations, at (416) 628-5936 x.5295.

Qualified Persons

The compilation of the Optimized LOM Plan was completed by Tysen Hantelmann, P.Eng. and Gord Doerksen, P.Eng of JDS Mining. By virtue of their education, membership to a recognized professional association and relevant work experience, Tysen Hantelmann and Gord Doerksen are independent Qualified Persons as defined by National Instrument 43-101 and have reviewed, approved and verified the technical content of this news release.

The mineral reserve estimates were prepared under the supervision of Tysen Hantelmann, P.Eng. and Gord Doerksen, P.Eng of JDS Mining. Mr. Hantelmann and Mr. Doerksen are a "qualified person" under NI 43-101 and is independent of the Company.  The mineral resource estimate for Rory's Knoll was prepared under the supervision of Tim Maunula, of T. Maunula & Associates Consulting. Mr. Maunula is a "qualified person" under NI 43-101 and is independent of the Company. The mineral resource estimates for the satellite deposits were prepared under the supervision of Daniel Noone of Guyana Goldfields Inc. Mr. Noone is a "qualified person" under National Instrument 43-101 and has also reviewed the contents of this press release.

About Guyana Goldfields Inc.:Guyana Goldfields Inc. is a Canadian based mid-tier gold producer primarily focused on the exploration, development and operation of gold deposits in Guyana, South America.

About Optimized LOM Plan Contributor:

About JDS Energy & Mining Inc.

JDS was founded in 2004 and is composed of a diverse set of skilled and highly experienced mining and construction professionals. With a proven record providing clients with fit-for-purpose solutions and value delivery, JDS has acquired a reputation for delivering and executing project plans on budget, on time, and most importantly, safely. The JDS team prides itself on delivering project concepts from inception to full operations – a process it has executed seamlessly for operations throughout Canada and worldwide.

Annual LOM Production Profile

Annual LOM Cost Profile

Non-IFRS Performance Measures

The Company has included certain non-IFRS performance measures in this press release including total cash costs per ounce and AISC per ounce. These measures are not defined under IFRS and should not be considered in isolation.  The Company believes that these measures, together with measures determined in accordance with IFRS, provide investors with an improved ability to evaluate the underlying performance of the Company. The inclusion of these measures is meant to provide additional information and should not be used as a substitute for performance measures prepared in accordance with IFRS. These measures are not necessarily standard and therefore may not be comparable to similar measures presented by other issuers. For a reconciliation of these numbers please refer to the Company's most recent management discussion and analysis.

Forwarding-Looking Information

This press release contains "forward-looking statements" and "forward-looking information" within the meaning of Canadian securities legislation. Forward-information includes, but is not limited to, statements with respect to mineral reserve and mineral resource estimates, mining operations and production, processing capacity, exploration and development activities, and cost estimates. Generally, forward-looking statements can be identified by the use of words and phrases such as "plans," "expects," "is expected," "budget," "scheduled," "estimates," "forecasts," "intends," "anticipates," or "believes" or variations (including negative variations) of such words and phrases, or statements that certain actions, events or results "may," "could," "would," "might" or "will" be taken, occur or be achieved.

Forward-looking statements are based on the reasonable assumptions, opinions, analysis and estimates of management as of the date such statements are made and are based on various assumptions regarding, among other things, the realization of mineral resource and mineral reserve estimates, currency fluctuations, gold metal prices, the timing and amount of future exploration and development expenditures, the estimation of initial and sustaining capital requirements, the estimation of labour and operating costs, the progress of exploration and development activities, the receipt of necessary regulatory approvals, and assumptions with respect to environmental risks, title disputes or claims, and other similar matters.

Forward-looking statements involve known and unknown risks, uncertainties and other factors which may cause the actual results, performance or achievements of the Company to be materially different from any future results, performance or achievements expressed or implied by the forward-looking statements. Such factors include, among others, the risks relating to the inability to realize mineral resource and mineral reserve estimates at anticipated recovery levels or at all, assumptions underlying mineral reserve and mineral resource estimates being incorrect, as well as those factors discussed in the section entitled "Risk Factors" in the Company's annual information form and management's discussion and analysis. Although the Company has attempted to identify important factors that could cause actual actions, events or results to differ materially from those described in forward looking statements, there may be other factors that cause actions, events or results to differ from those anticipated, estimated or intended.  Forward-looking statements contained herein are made as of the date of this press release and the Company disclaims any obligation to update any forward-looking information, except as may be required by applicable securities laws. There can be no assurance that forward-looking information will prove to be accurate, as actual results and future events could differ materially from those anticipated in such information. Accordingly, readers should not place undue reliance on forward-looking information.