"The mass grave contains the bodies of 73 people, men, women and children executed by the Islamic State group when they controlled the region," local official Chokor Melhem Elias told AFP.
He said Iraqi security forces made the latest discovery in the Rambussi area near the town of Qahtaniyya.
In 2014, IS killed thousands of Yazidis in Sinjar and kidnapped thousands of the community's women and girls as sex slaves.
Kurdish fighters backed by the US-led coalition recaptured Sinjar from IS in November 2015 before Iraqi security forces took control of the region in October.
As government troops have advanced across Iraq they have uncovered dozens of mass graves holding hundreds of bodies in areas that fell under the jihadists' brutal rule.
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