It is now the first lithium-producing operation outside Western Australia.
The company said after more than a year of construction its dense media separation plant had started production.
Concentrate will be stockpiled at site until Core generates sufficient volumes for haulage to the Darwin Port for first export.
That should happen in April to its foundation customers Ganfeng Lithium and Sichuan Yahua.
Not everything has gone smoothly, with ramp-up delays forecast.
Production has been impacted by heavy rainfalls over northern Australia in December, which has seen a significant volume of water in the base of the Grants pit that has impacted mining.
As a result, Core expects it won't achieve its full production target until after its original mid-year goal.
Finniss has reserves of 10.6 million tonnes grading 1.3% lithium oxide, with significant increases flagged by the company given its recent drilling successes.
Core will develop multiple deposits at Finniss to produce 197,000tpa of concentrate for sales over 12 years.
Noting today's achievement, Canaccord Genuity analysts Timothy Hoff and Reg Spencer believe production of 12,000t of spodumene by mid-year remains achievable by relying on already mined ore on the ROM pad.
With the wet season lasting until April, the pair forecasts production of 147,000t in financial 2024 at C1 cash costs of A$958/t, with any delayed already reflected in their estimates.
They see mining rates as a key focus over the next nine months to de-risk the production profile.
While lithium pricing has drifted lower due to softer demand from Chinese consumers and inventories being unwound, Canaccord said the price was broadly aligned with forecasts.
They believe Core is uses a concentrate price at a flat US$1550/t, compared to the spot price of $5800/t.
If the price remains elevated they expect earnings could lift 40% to A$34 million.
Core remains well-funded with $125 million cash and is expected to book revenue of $20 million from the sale of 15,000t of direct shipping ore material last month.
Canaccord has a ‘speculative buy' recommendation and a price target of $1.45 per share.
Core shares were off 4% this afternoon at 92.5c, capitalising it at $1.7 billion.
It has traded between 74c and $1.87 over the past year.
