He steps down immediately and the board said it was currently identifying and recruiting a suitable replacement.
Michael Masterman, W chairman, said: "I would like to thank Michael for his significant contribution to W over the past 10 years.
"His fantastic support and commitment to the company has helped steer us through the evolution of the business and he leaves us on strong footing with our Spanish and Portuguese tungsten and gold projects. We wish him continued success in his business ventures."
Last month, the firm revealed concentrate from its new tailings project at la Parrilla will have a much higher tungsten and tin content than originally forecast.