The fundamental difference is that consultancy can help you to resolve a job specific problem/situation you do not learn much yourself. Mentoring makes you understand the reasons behind the problem and enables you to take care of any such or similar situations in future. Mentoring is all about holistic learning and empowerment.

Mentors usually have many years of business experience and use this knowledge to look at the situation very objectively. They do not offer solutions but can help you analyze the situation and the solutions usually come from the client themselves as they are most knowledgeable about their own business. The mentors will generally guide you to work logically, show you the possible outcomes and use his/her experience to prompt some feasible solutions for you to look at. Mentors may not know about your specific professional work but definitely know the nuances of business.

Like discussing with your family doctor you need to share your full information with the mentor as only then can they know about your full picture. In this profession trust is the basic requirement and no personal information is disclosed to anyone else without the consent of the client.