My understanding is I have no capital gain, and would not be obliged to pay capital gain until I sold some more of the shares which I have left??
Forget about the cost of the parcel compared to the cost of the portion sold. You split the parcel into two amounts, those you have retained and those you have sold and allocate transactions costs proportionately. You then work out the capital gain on the portion you have sold compared to the acquisition costs of the portion you have sold (not the acquisition costs of the complete parcel).
So assume you bought 100 shares at $0.90 each and the brokerage (inc GST) was $10 (or $0.10 per share). You sell 60 for $2 each and brokerage (inc GST) is $10.
The 60 you sold realised $110 ($120 - $10 costs).
The cost of those 60 were $60 ($54 + $6 costs).
Your capital gain is $50. As Julia says, if you held for more than a year, you only add 50% of the CG to your income for tax purposes (e.g. $25).
The remaining 40 shares have a cost base of $40 for CGT calculation when they are eventually sold.
If you sell in one transaction shares that were part of several different parcels when bought, you identify which parcel they come from when determining the cost base. You don't have to follow any FIFO or LIFO rule if it doesn't suit you, so long as your records can adequately identify the source of each share sold. So if you have bought several parcels of the same share at different times and then sell a portion, if you want to reduce tax in the current year you might nominate the most costly as the source used in the sale or if you already have CG losses you may choose the least costly to write off against those losses or combinations thereof depending on what works best for you. Always bear in mind the 1 year rule, as it is usually better to sell those that are older than 1 year to get the 50% discount.