Heat coals or gas grill for direct heat. In 1-quart saucepan, mix marmalade, vinegar, oil, and sage. Cook over low heat about 1 minute, stirring occasionally, until well blended. Stir in chives.
Reserve ⅓ cup marmalade mixture to serve with chicken. Sprinkle chicken with garlic salt and pepper. Cover and grill over medium heat for 15 minutes; turn chicken.
Cover and grill 20 to 30 minutes longer, turning occasionally and brushing 2 or 3 times with marmalade mixture, until juice of chicken is no longer pink when centers of thickest pieces are cut. Serve reserved marmalade mixture with chicken.