Lithium exposure: Direct exposure to lithium can cause skin and mucous membrane irritation, including the lips. The black scabbed appearance could be due to lithium's caustic properties, leading to chemical burns.

Cobalt exposure: Cobalt is sometimes found in lithium mines and can cause skin lesions, dermatitis, and other skin problems, including lip lesions.
Nickel exposure: Nickel is another metal that may be present in lithium mines and can cause allergic contact dermatitis, which might manifest as black scabbed lips in severe cases.
Arsenic exposure: Arsenic can be found in some mining environments and is known to cause skin lesions and dermatitis, potentially leading to the observed symptoms.

Cancer (e.g., squamous cell carcinoma): Although less likely, it's crucial not to miss the possibility of cancer, especially if the lesions are persistent and not responding to treatment for exposure. Mining environments can expose workers to various carcinogens.
Infections (bacterial, fungal, or viral): Infections can cause similar symptoms, especially if the skin barrier is compromised due to chemical exposures. Failing to diagnose and treat an infection could lead to severe consequences.

Erythema multiforme: A skin condition that can be triggered by various factors, including infections and chemical exposures. It might present with lip lesions, although it's less common in this context.
Pellagra: A disease caused by niacin deficiency, which can lead to dermatitis, diarrhea, dementia, and potentially death if not treated. While rare and less directly related to mining exposures, it could be considered in cases of malnutrition or specific metabolic disorders exacerbated by occupational exposures.