Panmure Gordon has retained its 'buy' rating and 163p target price for FTSE 250 mining group Aquarius Platinum (AQP), but says that Monday's change in leadership presents a 'further challenge for the company already facing difficult market conditions'.The company has announced that Stuart Murray has resigned as Chief Executive Officer (CEO) of AQP and Chairman of principal subsidiary Aquarius Platinum South Africa (AQPSA). Meanwhile, Jean Nel has been appointed as Chief Operating Officer.Panmure analyst Alison Turner said: "Mr Murray has been CEO of Aquarius since September 2001, and is known for his hands-on leadership style. Until the appointment of Jean Nel to the AQP board as commercial director in March this year, Mr Murray was the sole board level executive (and in particular there was no board level finance director)."With Nel and Rob Schroder (Managing Director of AQPSA) only joining the group in January this year, Turner said that Murray's resignation leaves Aquarius in the hands of a "very new and thus largely untested" management team.Turner said that the company must "navigate the current precarious labour relations environment [...] and the pressures on its balance sheet in the absence of a CEO".Today's news follows the departure of CEOs at both Impala Platinum and Anglo Platinum earlier this year. Turner said that Murray's resignation is a "sign of the depth of the challenge of operating a platinum company in arguably the toughest conditions ever to have faced the industry." By 10:08, shares were down 8.95% at 43.25p.BC