I cut up a bunch of tails about a month ago and set the jars in the basement , looked at it today and noticed there is mold all over the top of the chunks . Is it ruined ?

Most organic meats, tissue etc. will break down and grow lots of various molds and fungi in the right environment. Until the oil begins to release they will continue to mold. Too late in the year to yield oil unless done with a heat source. I did a batch last winter on my wood stove. You need to keep an eye on it so it doesn't cook and remove it as it gets too hot etc.

Thanks can I freeze it and start again in the summer ?

put them in your hot box

an old dead fridge with light bulb

Yes you can freeze to stop the mold growth and begin again next summer if you are doing it the solar mehod.

Thanks .