any ideas ?, page-5

it would seem Zinc production is up at Perkoa as stated in 3rd Quarter Production Report from Glencore Xtrata.Press release dated 31 OCT 2013

"Other Zinc (AR Zinc, Los Quenuales, Sinchi Wayra, Rosh Pinah, Perkoa) This group produced 214,600 tonnes of own sourced zinc (metal and metal in concentrate),a 17% increase over the prior year. This increase relates to Rosh Pinah and Perkoa, partly offset by declines at Los Quenuales and Sinchi Wayradue to expected lower grades and some mining restrictions "

http://www.glencorexstrata.com/assets/Investors/GLEN-2013-IMS-and-Q3-Production-Report.pdf

Given the previous quarter contribution by Perkoa was 9200 tons of Zinc we dont know if the increase is comparing previous month or same period last year.
It would also seem that Glencore was expecting lower grades and decreases in production from other African Zinc sources.Looks like Perkoa is important to Glencore in maintaining its Zinc production in Africa.A relatively small operation (for them) to be specifically mention in 2 consecutive production report shows its importance.Also the vastly expanded mine was probably developed to address projected long term decreases in African Zinc production.