This is Vaishnavi, female energy of Vishnu, from Kerala region. Her upper hands are holding chakra (discuss) and shankha (conch shell). Typical attributes of Vishnu. Her lower hands are in Abhaya (protection) and Varada (boon bestowing) mudra. She is seated in padmasana on a circular base which in turn is supported by a robust rectangular platform.
Note the Sun and Moon in the prabhavali, just about Vaishnavi’s crown. Even her crown, middle part, has Sun and Moon symbols.
One noteworthy feature is the way the attributes are held, between the index and middle fingers. The ring finger is folded. This mudra is called Katarimukha, holding fingers like a pair of scissors.
Another unusual feature is the deity and the prabhavali is riveted to the base.
H K Sastri in his book on South Indian Images of Gods and Goddesses, page 191, identifies this Devi as Durga. My assigning the name Vaishnavi is as per the tradition in Kerala.
This was in a US diplomat’s collection till some time ago. It looks like the black colour was applied to simulate patina and it is starting wear out. The colour is quite uneven. Not sure about the age. Tha absence of ritual wear adds to the uncertainty about the age.